BAROMETERS.(‡ Bent Glass Tube.)FIG.1.(‡ Tube Immersed In Mercury.)FIG.2.(‡ Weather Glasses.)FIG.3.The barometer is designed to indicate the weight or pressure of the air on any surface, at any particular time or place; for the air, although invisible, is still of considerable weight, as there are many miles of it pressing from above downwards on all parts of everything upon the earth, and the barometer is for the purpose of ascertaining how much this pressure amounts to. It is formed as follows: a piece of glass tubing, about three feet long, is first closed at one end, then turned up at the other and expanded (fig. 1); when this tube is filled with mercury and held with the bulb downwards, the mercury sinks in the stalk to a certain height (say twenty-nine inches), and that height shows the weight or pressure of the air. The reason of this will be understood by supposing a piece of straight glass tubing, three feet long, to be closed at one end and then filled with mercury; if the finger be placed on the end not closed, and that end turned downwards and put into a basin of mercury (fig. 2) before the finger is withdrawn, the fluid, if the air exerted no pressure, would all sink down from the inside of the tube into that in the basin, leaving a “vacuum” or empty space in the hollow of the tube, but it is evident if the air exerted any pressure on the surface of the mercury in the basin, this pressure would force the mercury up the tube (for there is no opposing pressure in an empty space), and that the mercury would rise higher and higher the greater the the pressure. Well, then, the air really exerts this pressure, and to such an extent as to raise the mercury somewhere about thirty inches in height, and the pressure necessary to do this is found by calculation to be about fifteen pounds upon every square inch of surface. The barometer tube is divided into a scale of inches and fractions of inches. What are called weather glasses, are barometers having the lower part brought up by a curve, and a small weight resting on the mercury in it, which being attached to a corresponding weight by means of a cord running over a little wheel or pulley fixed to hands moving round a sort of dial, turns them as the mercury rises or sinks (fig. 3), for as the mercury falls in the stalk it must of course rise in the short stalk of the curve; the hands by these means are turned round, and the rise or fall of the fluid will cause them to point to “fair,” “rain,” &c., as the case may be, for these names are marked where a corresponding change of the weather may so influence the weight of the air, as to raise or depress the mercury, and so bring the hands in a position to point to them.
(‡ Bent Glass Tube.)FIG.1.(‡ Tube Immersed In Mercury.)FIG.2.(‡ Weather Glasses.)FIG.3.
(‡ Bent Glass Tube.)FIG.1.
FIG.1.
(‡ Tube Immersed In Mercury.)FIG.2.
FIG.2.
(‡ Weather Glasses.)FIG.3.
FIG.3.
The barometer is designed to indicate the weight or pressure of the air on any surface, at any particular time or place; for the air, although invisible, is still of considerable weight, as there are many miles of it pressing from above downwards on all parts of everything upon the earth, and the barometer is for the purpose of ascertaining how much this pressure amounts to. It is formed as follows: a piece of glass tubing, about three feet long, is first closed at one end, then turned up at the other and expanded (fig. 1); when this tube is filled with mercury and held with the bulb downwards, the mercury sinks in the stalk to a certain height (say twenty-nine inches), and that height shows the weight or pressure of the air. The reason of this will be understood by supposing a piece of straight glass tubing, three feet long, to be closed at one end and then filled with mercury; if the finger be placed on the end not closed, and that end turned downwards and put into a basin of mercury (fig. 2) before the finger is withdrawn, the fluid, if the air exerted no pressure, would all sink down from the inside of the tube into that in the basin, leaving a “vacuum” or empty space in the hollow of the tube, but it is evident if the air exerted any pressure on the surface of the mercury in the basin, this pressure would force the mercury up the tube (for there is no opposing pressure in an empty space), and that the mercury would rise higher and higher the greater the the pressure. Well, then, the air really exerts this pressure, and to such an extent as to raise the mercury somewhere about thirty inches in height, and the pressure necessary to do this is found by calculation to be about fifteen pounds upon every square inch of surface. The barometer tube is divided into a scale of inches and fractions of inches. What are called weather glasses, are barometers having the lower part brought up by a curve, and a small weight resting on the mercury in it, which being attached to a corresponding weight by means of a cord running over a little wheel or pulley fixed to hands moving round a sort of dial, turns them as the mercury rises or sinks (fig. 3), for as the mercury falls in the stalk it must of course rise in the short stalk of the curve; the hands by these means are turned round, and the rise or fall of the fluid will cause them to point to “fair,” “rain,” &c., as the case may be, for these names are marked where a corresponding change of the weather may so influence the weight of the air, as to raise or depress the mercury, and so bring the hands in a position to point to them.
PENDULUMS.(‡ Gridiron Pendulum.)FIG.1.(‡ Mercurial Pendulum.)FIG.2.Any weight attached to a rod or wire so that it can swing freely may be called a “pendulum.” But for the purpose of time-keeping, a much more accurate instrument is required; the rate of vibration or oscillation of the pendulum, does not depend upon the weight of the ball or “bob” at the lower end, but upon the distance of this from the point at which the upper end turns, nor does the rate of oscillation depend upon the distance through which the weight traverses, for every pendulum will vibrate at the exact rate (with certain restrictions) at which it is set off, until it ceases, although the distance through which it traverses, decreases at every vibration; these facts are taken advantage of in adapting the pendulum to the purposes of regulating the time a clock shall keep—the longer the pendulum the slower the vibrations. Now, as everything in nature is expanded by heat and contracted by cold, so a pendulum is constantly varying in length by every change of temperature, and, as a consequence, the rate of the clock to which it is attached will also vary. Pendulums which have an arrangement to obviate this variation, are called “compensating” pendulums; the best in use are of two kinds, one called (from its appearance) the “gridiron,” the other the “mercurial,” this last is the most accurate, and is used in nearly all good astronomical clocks. The gridiron pendulum is made of iron and brass, or zinc, and is constructed as shown infig. 1; the rod and outer frame,A, is made of iron, the two rods inside this of zinc or brass,B B. The principle of the instrument is this—brass or zinc contract and expand much more than iron does, and the short bars of these metals will expand or contract as much as the long bar of iron forming the rod of the pendulum, so that as this expands and lets the “bob” down, the short bars expand and draw it upwards so that it keeps its place at any temperature; this requires very accurate adjustment. The mercurial pendulum is shown atfig. 2; it is on the same principle, but is easier to regulate, and more manageable, the vessel in the centre being partly filled with mercury, and forming the weight itself, and thus as the mercury expands upwards it compensates for the elongation of the rod, the same as in the gridiron pendulum.The nearer any pendulum is to the centre of the earth the more quickly does it vibrate; this has been used by scientific men, to determine by the difference of rate in one placed on a hill, and another at the bottom of a deep mine, the amount of matter which constitutes our globe; indeed by these trials the world may fairly be said to have been weighed!
(‡ Gridiron Pendulum.)FIG.1.
FIG.1.
(‡ Mercurial Pendulum.)FIG.2.
FIG.2.
Any weight attached to a rod or wire so that it can swing freely may be called a “pendulum.” But for the purpose of time-keeping, a much more accurate instrument is required; the rate of vibration or oscillation of the pendulum, does not depend upon the weight of the ball or “bob” at the lower end, but upon the distance of this from the point at which the upper end turns, nor does the rate of oscillation depend upon the distance through which the weight traverses, for every pendulum will vibrate at the exact rate (with certain restrictions) at which it is set off, until it ceases, although the distance through which it traverses, decreases at every vibration; these facts are taken advantage of in adapting the pendulum to the purposes of regulating the time a clock shall keep—the longer the pendulum the slower the vibrations. Now, as everything in nature is expanded by heat and contracted by cold, so a pendulum is constantly varying in length by every change of temperature, and, as a consequence, the rate of the clock to which it is attached will also vary. Pendulums which have an arrangement to obviate this variation, are called “compensating” pendulums; the best in use are of two kinds, one called (from its appearance) the “gridiron,” the other the “mercurial,” this last is the most accurate, and is used in nearly all good astronomical clocks. The gridiron pendulum is made of iron and brass, or zinc, and is constructed as shown infig. 1; the rod and outer frame,A, is made of iron, the two rods inside this of zinc or brass,B B. The principle of the instrument is this—brass or zinc contract and expand much more than iron does, and the short bars of these metals will expand or contract as much as the long bar of iron forming the rod of the pendulum, so that as this expands and lets the “bob” down, the short bars expand and draw it upwards so that it keeps its place at any temperature; this requires very accurate adjustment. The mercurial pendulum is shown atfig. 2; it is on the same principle, but is easier to regulate, and more manageable, the vessel in the centre being partly filled with mercury, and forming the weight itself, and thus as the mercury expands upwards it compensates for the elongation of the rod, the same as in the gridiron pendulum.
The nearer any pendulum is to the centre of the earth the more quickly does it vibrate; this has been used by scientific men, to determine by the difference of rate in one placed on a hill, and another at the bottom of a deep mine, the amount of matter which constitutes our globe; indeed by these trials the world may fairly be said to have been weighed!
PLOUGHS.Ploughs are instruments used to perform more rapidly what may be effected by the spade, namely, the cutting-up and turning-over the surface of the ground so as to destroy all grass and weeds growing in it, loosen, so as to expose it to the influence of the air, and render it fit to receive the seed.(‡ Plough.)The plough has been in use from the very earliest ages, and has been but little altered for many centuries; it is drawn by horses attached to the chainAat the end of the “beam,” and guided by a man holding the “stilts” or handlesB B, the coulter,C, cuts a perpendicular slice in the ground, and the “share” or “slade,”D, following, cuts horizontally, so as to separate a long piece of earth which the breast or mould-boardE, placed obliquely, turns over on one side; the plough returning at regular distances, successive cuttings are thus laid side by side, forming narrow ridges;Fis an additional coulter called the “skim-coulter,” for removing the surface of the earth, and is only occasionally used.There are a great many kinds of ploughs, each suitable to the kind of soil to be ploughed, whether light and dry or heavy and moist.
Ploughs are instruments used to perform more rapidly what may be effected by the spade, namely, the cutting-up and turning-over the surface of the ground so as to destroy all grass and weeds growing in it, loosen, so as to expose it to the influence of the air, and render it fit to receive the seed.
(‡ Plough.)
The plough has been in use from the very earliest ages, and has been but little altered for many centuries; it is drawn by horses attached to the chainAat the end of the “beam,” and guided by a man holding the “stilts” or handlesB B, the coulter,C, cuts a perpendicular slice in the ground, and the “share” or “slade,”D, following, cuts horizontally, so as to separate a long piece of earth which the breast or mould-boardE, placed obliquely, turns over on one side; the plough returning at regular distances, successive cuttings are thus laid side by side, forming narrow ridges;Fis an additional coulter called the “skim-coulter,” for removing the surface of the earth, and is only occasionally used.
There are a great many kinds of ploughs, each suitable to the kind of soil to be ploughed, whether light and dry or heavy and moist.
HARROWS.HARROW.These instruments are used to stir up, pulverise, and mix together the earth, also to tear up any roots that may be left after ploughing, and to cover up the seed after sowing. The cut represents the usual form of harrow, having a number of iron spikes or teeth attached to frames of which two or more are united together by chains and attached to a bar, that the horses may drag them over the surface of the soil.Bush-harrows consist of a bundle of brush-wood held together by a pair of frames, and drawn over the soil when it is very dry and light; they are used chiefly to cover up the seed after “drilling.”
HARROW.
HARROW.
These instruments are used to stir up, pulverise, and mix together the earth, also to tear up any roots that may be left after ploughing, and to cover up the seed after sowing. The cut represents the usual form of harrow, having a number of iron spikes or teeth attached to frames of which two or more are united together by chains and attached to a bar, that the horses may drag them over the surface of the soil.
Bush-harrows consist of a bundle of brush-wood held together by a pair of frames, and drawn over the soil when it is very dry and light; they are used chiefly to cover up the seed after “drilling.”
ROLLERS.(‡ Undulated Rollers.)In clay and other heavy soils, it is necessary after ploughing to break up the large pieces by means of rollers, and in light soils to press it together; for these purposes rollers are used, either with smooth or undulated surfaces, as in the figure; these last form furrows into which the seed falls, causing it to come up in rows. Rollers of a lighter kind are used after mowing to level the surface.
(‡ Undulated Rollers.)
In clay and other heavy soils, it is necessary after ploughing to break up the large pieces by means of rollers, and in light soils to press it together; for these purposes rollers are used, either with smooth or undulated surfaces, as in the figure; these last form furrows into which the seed falls, causing it to come up in rows. Rollers of a lighter kind are used after mowing to level the surface.
MOWING MACHINES.(‡ Scythe.)FIG.1.(‡ Dray Mowing Machine.)FIG.2.Mowing is an operation generally performed by manual labour, by means of that well-known instrument, the scythe (fig. 1), which is a long, flat, curved blade of steel attached to a handle having a peculiar bend, and with two short pieces of wood attached, by which the mower swings it round with a measured sweep, cutting off the grass almost close to the ground, walking gradually forward as he mows; but of late years machines of various kinds have been invented and used for this purpose.Fig. 2represents one which not only mows, but at the same time rolls the grass, so as to make it smooth and level. It consists of a heavy iron roller turning a large wheel, which, being united to a small one, causes it to revolve very rapidly. In connection with the small wheel is a series of four spiral knives wound round a cylinder, which cut off the grass close to the ground, throwing it up into a box placed to receive it. There are several varieties, but this is the kind made by Dray & Co., London, for mowing short grass, as in gardens and lawns. Those used for cutting long grass for hay, are exactly similar to the reaping machines.
(‡ Scythe.)FIG.1.
FIG.1.
(‡ Dray Mowing Machine.)FIG.2.
FIG.2.
Mowing is an operation generally performed by manual labour, by means of that well-known instrument, the scythe (fig. 1), which is a long, flat, curved blade of steel attached to a handle having a peculiar bend, and with two short pieces of wood attached, by which the mower swings it round with a measured sweep, cutting off the grass almost close to the ground, walking gradually forward as he mows; but of late years machines of various kinds have been invented and used for this purpose.Fig. 2represents one which not only mows, but at the same time rolls the grass, so as to make it smooth and level. It consists of a heavy iron roller turning a large wheel, which, being united to a small one, causes it to revolve very rapidly. In connection with the small wheel is a series of four spiral knives wound round a cylinder, which cut off the grass close to the ground, throwing it up into a box placed to receive it. There are several varieties, but this is the kind made by Dray & Co., London, for mowing short grass, as in gardens and lawns. Those used for cutting long grass for hay, are exactly similar to the reaping machines.
THRASHING-MACHINES.(‡ Thrashing Machine.)The operation of thrashing, performed for ages by means of the “flail”—two sticks tied together and wielded by the hands, inflicting heavy blows on the bundle of corn spread on the thrashing-floor, so as to separate the grains from the ear—is now being rapidly superseded by the thrashing-machine. It is a sort of box having a cylinder inside with an iron wheel at each end united by bars of iron; this wheel revolves by steam, causing the bars to fall upon the corn with a gliding motion, thrashing out the grain, which falls through and is received below.
(‡ Thrashing Machine.)
The operation of thrashing, performed for ages by means of the “flail”—two sticks tied together and wielded by the hands, inflicting heavy blows on the bundle of corn spread on the thrashing-floor, so as to separate the grains from the ear—is now being rapidly superseded by the thrashing-machine. It is a sort of box having a cylinder inside with an iron wheel at each end united by bars of iron; this wheel revolves by steam, causing the bars to fall upon the corn with a gliding motion, thrashing out the grain, which falls through and is received below.
REAPING MACHINES.REAPING MACHINE.SICKLE.Machines have lately been produced to effect more rapidly, what has hitherto been done by hand, with the sickle, namely, the reaping of corn. These machines are of various kinds, but the one that seems most perfect has been patented by Messrs. Dray & Co.; it consists of a heavy wooden frame drawn by a horse, and having wheels attached, which on turning round set in motion a line of spear-headed knives; these knives are made sharp at each side, to cut both ways. The motion communicated to them is very rapid, and from side to side, so as to cause the knives to pass through long narrow openings made to fit them in a series of iron points which are placed one between each knife. This action causes the point and knife to act like the blades of a pair of scissors, only that the points are fixed and the blades move through them, cutting off the corn at any distance from the ground that may be required; at the side furthest from the horse is a point of iron, having two diverging pieces prolonged from it, and which pierces the corn and separates the portion to be cut from what is to be cut at the next return of the machine; for it is drawn up and down, cutting at each time a belt about four or five feet wide; when cut, the corn falls on a platform balanced on its centre, and capable of being turned so as to incline forwards or backwards. A man sits on the machine with a rake, and as the platform fills with cut corn, he pushes it with the rake, tilting the platform back and delivering the corn behind, where women attend to bind it up. These machines can reap ten or eleven acres in a day.
REAPING MACHINE.
REAPING MACHINE.
SICKLE.
SICKLE.
Machines have lately been produced to effect more rapidly, what has hitherto been done by hand, with the sickle, namely, the reaping of corn. These machines are of various kinds, but the one that seems most perfect has been patented by Messrs. Dray & Co.; it consists of a heavy wooden frame drawn by a horse, and having wheels attached, which on turning round set in motion a line of spear-headed knives; these knives are made sharp at each side, to cut both ways. The motion communicated to them is very rapid, and from side to side, so as to cause the knives to pass through long narrow openings made to fit them in a series of iron points which are placed one between each knife. This action causes the point and knife to act like the blades of a pair of scissors, only that the points are fixed and the blades move through them, cutting off the corn at any distance from the ground that may be required; at the side furthest from the horse is a point of iron, having two diverging pieces prolonged from it, and which pierces the corn and separates the portion to be cut from what is to be cut at the next return of the machine; for it is drawn up and down, cutting at each time a belt about four or five feet wide; when cut, the corn falls on a platform balanced on its centre, and capable of being turned so as to incline forwards or backwards. A man sits on the machine with a rake, and as the platform fills with cut corn, he pushes it with the rake, tilting the platform back and delivering the corn behind, where women attend to bind it up. These machines can reap ten or eleven acres in a day.
DRILLS.DRILL.The drill is used when it is desirable to sow seed in rows at intervals from each other, so as to give room for the plants to grow, to free them from weeds and admit air, light, and moisture; it is a machine which contains the seed for sowing, and at the same time makes a series of furrows to receive it. There are a great many varieties of drills, but they act upon the same principle, namely, that of a cylinder, taking up and pouring small portions of the seed into funnels so arranged that they shall follow a set of small coulters forming furrows in the ground, into which the seed falls; the drill is generally followed by a bush-harrow which covers up the seed. Some drills have two compartments, one for containing manure, the other for seed; the manure must be dry and pulverised, such as ground bones, ashes, &c., which arrangement allows the seed and manure to be both drilled together, so that the manure shall only be applied where it is wanted. The cut represents this machine;A Aare portions of the cylinders which are turned round by toothed wheels attached to the ordinary wheels of the machine, and which can be put in or out of gear at any time, so as to stop the action of the drill;B Brepresent the funnels into which the seed is poured, andC Cthe coulters which cut the furrows for the seed. These coulters are pressed into the ground by means of iron weights attached to the ends of levers joined to them, and which can be regulated by small chains.
DRILL.
DRILL.
The drill is used when it is desirable to sow seed in rows at intervals from each other, so as to give room for the plants to grow, to free them from weeds and admit air, light, and moisture; it is a machine which contains the seed for sowing, and at the same time makes a series of furrows to receive it. There are a great many varieties of drills, but they act upon the same principle, namely, that of a cylinder, taking up and pouring small portions of the seed into funnels so arranged that they shall follow a set of small coulters forming furrows in the ground, into which the seed falls; the drill is generally followed by a bush-harrow which covers up the seed. Some drills have two compartments, one for containing manure, the other for seed; the manure must be dry and pulverised, such as ground bones, ashes, &c., which arrangement allows the seed and manure to be both drilled together, so that the manure shall only be applied where it is wanted. The cut represents this machine;A Aare portions of the cylinders which are turned round by toothed wheels attached to the ordinary wheels of the machine, and which can be put in or out of gear at any time, so as to stop the action of the drill;B Brepresent the funnels into which the seed is poured, andC Cthe coulters which cut the furrows for the seed. These coulters are pressed into the ground by means of iron weights attached to the ends of levers joined to them, and which can be regulated by small chains.
ENGINEERING WORKS.RAILWAYS.(‡ Locomotive And Tender.)The great advantage of railways over ordinary roads is the diminished friction, which is produced by the wheels passing over the smooth iron instead of rough stones. It was found when iron rails were first used, before the introduction of locomotives, that the horse-power requisite was diminished to one-fortieth; for instance, ten horses on a railway could do the work of four hundred on a common road, this being the case, and the great power of the locomotive engine being superadded, there can be no wonder that the difference of the rate of speed between the train and the wagon should be so great. When it has been settled what general direction the railway shall take, it is then to be determined whether or to what extent the elevations or depressions that may occur can be conveniently overcome, so that the line may take a straight course, or whether the road shall go out of the straight line, and how far to avoid them. The route it should therefore take ought to exactly balance the objections to each extreme, that is the expense, &c., of going straight on through hills and over valleys on the one side, and the increased distance and consequent loss of time which a winding track would cause to the transit on the other.(‡ Terrain Schematic.)FIG.1.(‡ Terrain Schematic.)FIG.2.(‡ Rail Types.)FIG.3.(‡ Rail “Chair.”)FIG.4.With respect to the “level” at which the line should be laid, a section of the route, showing all the elevations and depressions, is first made, then such a course is chosen that the material produced by cutting through the higher parts shall be just sufficient to form the embankments for filling up the lower parts;fig. 1will give some idea of this arrangement. Of course a line perfectly level would be the best, just as would be one perfectly straight; but as the difficulties of the one must be balanced, so must those of the other, and a line as nearly level should be obtained as is consistent with expense. For instance, supposeAandB,fig. 2, to be towns to be connected by a line of railway, and the chief of the intermediate ground to be above their level; of course it would be very expensive to cut through the whole distance, as shown at the dotted linea, this level would therefore be too low; but if a higher level were taken, as at the dotted lineb, then only the centre of the distance would have to be cut through, and the material (earth, &c.) produced by the cuttings would suffice to fill up the hollows at the ends. These considerations and many others must therefore determine the level at which the railway shall be constructed; but the line is seldom (if ever) on one level from end to end, nor at one continuous “gradient” or slope, for the course of the line is so arranged as to make as little cutting and filling up as is consistent with a road whose gradients shall never exceed a specified amount, which must be determined by local circumstances. The excavation and filling up being finished, the “trams” have to be laid; these are bars of wrought iron about fifteen feet long, of the form shown atAandB,fig. 3. The most usual form is that markedA. They are made of wrought-iron, passed while hot between rollers cut at their edges into the form required. These trams are laid upon bars of wood called “sleepers,” at about four feet apart, and united to them by what are called “chairs,” which are pieces of cast-iron of the form shown atfig. 4, fastened to the sleepers by iron spikes, and into these the trams, or “metals,” as they are called by the workmen are wedged. These bars of iron are laid very evenly and perfectly parallel at a certain distance apart, which must exactly correspond to the distance between each wheel of a pair belonging to the carriages and engines; this distance is called the “gauge,” the wide gauge (as on the Great Western) is seven feet, and that called the “narrow gauge,” is four feet eight-and-a-half inches, and the space between the lines is of sufficient width to prevent any danger of collision in the trains on passing each other; they are generally six feet apart.(‡ Railway Switch.)FIG.5.(‡ Turn-Tables.)FIG.6.(‡ Wheel With Flange.)FIG.8.(‡ Locomotive On Turn-Table.)FIG.7.(‡ Carriage Buffer.)FIG.9.(‡ Carriage Buffer.)FIG.10.As it is necessary that trains should at certain places be “shunted” or shifted from one line of rails to another, particularly at stations where a great many tracks run side by side, and cross each other to branch off to different parts, there are arrangements called “points,” shifted by a lever or “switch,” so that they shall direct the course of the train, and cause it to leave the former track and enter upon a new one; this arrangement may be seen atfig. 5, where the points are in the position to direct the engine coming in the direction of the arrow on to the curved lineA, and the dotted lines indicate the position into which they would be shifted, if necessary for the train to go straight on to the lineB; this action is effected by moving a lever which shifts the two bars a few inches either way. When an engine or carriage has to be turned on to a track at right angles to the one on which it rests, or where there is not room for “shunting,” an apparatus called a “turn-table” is used, which is shown atfigs. 6and7; it is a round platform of iron turning on its centre, and supported by friction rollers at the edge, having on its surface raised rails in two or more directions, so that it may be turned round half or quarter distance, according to the position required. The engines and carriages used to run on railways are of various constructions, but to a certain extent agree in their chief particulars; the wheels are fixed to their axles, so that each pair and the axle which joins them may be considered as one piece.The axle projects a little way beyond the wheel, and on this part it supports the engine or carriage, which is wider than the distance from one wheel to its fellow. They are therefore entirely underneath. They are of iron, made by machinery and have a projecting edge on the inside of the “tire” of each, which is called the “flange” (seefig. 8); this flange does not run on the rail but within it to prevent the wheels from slipping off. These flanges, when the pair of wheels and axle are united, exactly fit in between the rails, so as to touch the inside of each and form a sort of guide. Each carriage has two pairs (except in a few cases, where three pairs are used), the engines have usually three, and sometimes four pairs. The carriages rest upon powerful springs, and are moreover furnished with springs to diminish the concussion of one carriage against another; these last are acted on by a sort of piston-rod, one of which is placed at each corner of the carriage, and are called “buffers” (figs. 9and10); they all coincide with each other, and form a set of springs all along the train, which greatly reduces the shock which would otherwise be felt when it is stopped. Another set of springs is connected with the binding screws which unite each carriage, and these prevent the sudden jerk which would result from the starting off of a train quite inelastic in its length.The engines used are of that class called high-pressure or non-condensing, and there are two cylinders and pistons, which have a stroke of about eighteen inches. The boiler is so contrived that a large quantity of steam shall be rapidly produced; for this purpose tubes of brass are made to pass side by side from the fireplace through the boiler, and through these tubes the flame and hot air must go before reaching the funnel, giving out in its course a great amount of heat to the water and converting it rapidly into steam. The steam from each cylinder passes at each stroke of the piston into the funnel, assisting to form a draught which draws the flame from the fire through the tubes and increases the fierceness of the combustion. The necessity for two cylinders and pistons is owing to the impossibility of having a fly-wheel, and as the driving wheels of the engine have to be turned at an equal rate, the axle has two cranks so placed that the greatest power of one piston is exerted where the other exerts the least (see “Steam-engine”).(‡ Signal Tower.)FIG.11.(‡ Signal Tower.)FIG.12.(‡ Signal Lamps.)FIG.13.As the trains when going at a considerable speed cannot be suddenly stopped, it is necessary to have signals placed in certain conspicuous positions, that the engine driver may begin to stop the train (when necessary) in time; this he effects by what is called a “break,” a contrivance by which two pieces of wood are made (by turning a screw) to grasp firmly each of a pair of wheels, and so prevent them turning round, this produces so much friction against the trams that (after the steam is turned off) the onward motion of the train is soon stopped. The signals are of three kinds generally, a red flag to indicate danger, a green one to caution, and a white one to show that the way is clear; these are (on most occasions) held by a man and waved to and fro to attract attention, but there are however a great many occasions for fixed signals, as at stations and bends in the line where the engine driver can only see a short distance ahead; these fixed signals consist of tall posts placed where they can be seen at a considerable distance. These posts have an arrangement at the top consisting of a lamp with a “bull’s-eye” or lens at each side pointing up and down the line, and a pair of arms capable of being let down into the post, raised at right angles with it, or into a position midway between the post and a right angle (as shown infigs. 11and12). One side of each arm is painted red, the other white, one arm serving for a signal up the line and the other down; attached to the joint of each arm, close to the post, are two iron frames each holding a piece of colored glass, one red the other green, and so arranged that when the arm is at right angles to the post, the red glass is before the lamp and when the arm is let half way down the green glass comes in front of the lamp (fig. 13), thus the same action serves both for day and night signals. When the arm showing the red side projects in a horizontal direction, it indicates (in the day) “danger,” and so does the red light at night; when the arm is let down half way, it shows that caution is required, and the green glass then before the lamp shows the same signal at night; when the arm is let quite down out of sight, it shows safety, and so does the white light of the lamp thus freed from both screens of colored glass.(‡ Engine Whistle.)FIG.14.Each engine is provided with a whistle (fig. 14)blown by steam turned on from the boiler, which is used as a signal at any particular time, especially in tunnels or when there is a fog; there is also an arrangement by which each engine presses on a lever at the side of the tram as it passes, and causes a bell to ring at the station, to announce its approach, when about a quarter of a mile off. In some cases, as in foggy weather, when the usual signals cannot be seen, a packet of fulminating powder is placed on the rail, and this being exploded by the wheel of the engine as it passes over it, gives notice of its approach, &c. There are other signals, but these are the chief.
(‡ Locomotive And Tender.)
The great advantage of railways over ordinary roads is the diminished friction, which is produced by the wheels passing over the smooth iron instead of rough stones. It was found when iron rails were first used, before the introduction of locomotives, that the horse-power requisite was diminished to one-fortieth; for instance, ten horses on a railway could do the work of four hundred on a common road, this being the case, and the great power of the locomotive engine being superadded, there can be no wonder that the difference of the rate of speed between the train and the wagon should be so great. When it has been settled what general direction the railway shall take, it is then to be determined whether or to what extent the elevations or depressions that may occur can be conveniently overcome, so that the line may take a straight course, or whether the road shall go out of the straight line, and how far to avoid them. The route it should therefore take ought to exactly balance the objections to each extreme, that is the expense, &c., of going straight on through hills and over valleys on the one side, and the increased distance and consequent loss of time which a winding track would cause to the transit on the other.
(‡ Terrain Schematic.)FIG.1.
FIG.1.
(‡ Terrain Schematic.)FIG.2.
FIG.2.
(‡ Rail Types.)FIG.3.(‡ Rail “Chair.”)FIG.4.
(‡ Rail Types.)FIG.3.
FIG.3.
(‡ Rail “Chair.”)FIG.4.
FIG.4.
With respect to the “level” at which the line should be laid, a section of the route, showing all the elevations and depressions, is first made, then such a course is chosen that the material produced by cutting through the higher parts shall be just sufficient to form the embankments for filling up the lower parts;fig. 1will give some idea of this arrangement. Of course a line perfectly level would be the best, just as would be one perfectly straight; but as the difficulties of the one must be balanced, so must those of the other, and a line as nearly level should be obtained as is consistent with expense. For instance, supposeAandB,fig. 2, to be towns to be connected by a line of railway, and the chief of the intermediate ground to be above their level; of course it would be very expensive to cut through the whole distance, as shown at the dotted linea, this level would therefore be too low; but if a higher level were taken, as at the dotted lineb, then only the centre of the distance would have to be cut through, and the material (earth, &c.) produced by the cuttings would suffice to fill up the hollows at the ends. These considerations and many others must therefore determine the level at which the railway shall be constructed; but the line is seldom (if ever) on one level from end to end, nor at one continuous “gradient” or slope, for the course of the line is so arranged as to make as little cutting and filling up as is consistent with a road whose gradients shall never exceed a specified amount, which must be determined by local circumstances. The excavation and filling up being finished, the “trams” have to be laid; these are bars of wrought iron about fifteen feet long, of the form shown atAandB,fig. 3. The most usual form is that markedA. They are made of wrought-iron, passed while hot between rollers cut at their edges into the form required. These trams are laid upon bars of wood called “sleepers,” at about four feet apart, and united to them by what are called “chairs,” which are pieces of cast-iron of the form shown atfig. 4, fastened to the sleepers by iron spikes, and into these the trams, or “metals,” as they are called by the workmen are wedged. These bars of iron are laid very evenly and perfectly parallel at a certain distance apart, which must exactly correspond to the distance between each wheel of a pair belonging to the carriages and engines; this distance is called the “gauge,” the wide gauge (as on the Great Western) is seven feet, and that called the “narrow gauge,” is four feet eight-and-a-half inches, and the space between the lines is of sufficient width to prevent any danger of collision in the trains on passing each other; they are generally six feet apart.
(‡ Railway Switch.)FIG.5.
FIG.5.
(‡ Turn-Tables.)FIG.6.(‡ Wheel With Flange.)FIG.8.
(‡ Turn-Tables.)FIG.6.
FIG.6.
(‡ Wheel With Flange.)FIG.8.
FIG.8.
(‡ Locomotive On Turn-Table.)FIG.7.(‡ Carriage Buffer.)FIG.9.(‡ Carriage Buffer.)FIG.10.
(‡ Locomotive On Turn-Table.)FIG.7.
FIG.7.
(‡ Carriage Buffer.)FIG.9.
FIG.9.
(‡ Carriage Buffer.)FIG.10.
FIG.10.
As it is necessary that trains should at certain places be “shunted” or shifted from one line of rails to another, particularly at stations where a great many tracks run side by side, and cross each other to branch off to different parts, there are arrangements called “points,” shifted by a lever or “switch,” so that they shall direct the course of the train, and cause it to leave the former track and enter upon a new one; this arrangement may be seen atfig. 5, where the points are in the position to direct the engine coming in the direction of the arrow on to the curved lineA, and the dotted lines indicate the position into which they would be shifted, if necessary for the train to go straight on to the lineB; this action is effected by moving a lever which shifts the two bars a few inches either way. When an engine or carriage has to be turned on to a track at right angles to the one on which it rests, or where there is not room for “shunting,” an apparatus called a “turn-table” is used, which is shown atfigs. 6and7; it is a round platform of iron turning on its centre, and supported by friction rollers at the edge, having on its surface raised rails in two or more directions, so that it may be turned round half or quarter distance, according to the position required. The engines and carriages used to run on railways are of various constructions, but to a certain extent agree in their chief particulars; the wheels are fixed to their axles, so that each pair and the axle which joins them may be considered as one piece.The axle projects a little way beyond the wheel, and on this part it supports the engine or carriage, which is wider than the distance from one wheel to its fellow. They are therefore entirely underneath. They are of iron, made by machinery and have a projecting edge on the inside of the “tire” of each, which is called the “flange” (seefig. 8); this flange does not run on the rail but within it to prevent the wheels from slipping off. These flanges, when the pair of wheels and axle are united, exactly fit in between the rails, so as to touch the inside of each and form a sort of guide. Each carriage has two pairs (except in a few cases, where three pairs are used), the engines have usually three, and sometimes four pairs. The carriages rest upon powerful springs, and are moreover furnished with springs to diminish the concussion of one carriage against another; these last are acted on by a sort of piston-rod, one of which is placed at each corner of the carriage, and are called “buffers” (figs. 9and10); they all coincide with each other, and form a set of springs all along the train, which greatly reduces the shock which would otherwise be felt when it is stopped. Another set of springs is connected with the binding screws which unite each carriage, and these prevent the sudden jerk which would result from the starting off of a train quite inelastic in its length.
The engines used are of that class called high-pressure or non-condensing, and there are two cylinders and pistons, which have a stroke of about eighteen inches. The boiler is so contrived that a large quantity of steam shall be rapidly produced; for this purpose tubes of brass are made to pass side by side from the fireplace through the boiler, and through these tubes the flame and hot air must go before reaching the funnel, giving out in its course a great amount of heat to the water and converting it rapidly into steam. The steam from each cylinder passes at each stroke of the piston into the funnel, assisting to form a draught which draws the flame from the fire through the tubes and increases the fierceness of the combustion. The necessity for two cylinders and pistons is owing to the impossibility of having a fly-wheel, and as the driving wheels of the engine have to be turned at an equal rate, the axle has two cranks so placed that the greatest power of one piston is exerted where the other exerts the least (see “Steam-engine”).
(‡ Signal Tower.)FIG.11.(‡ Signal Tower.)FIG.12.
(‡ Signal Tower.)FIG.11.
FIG.11.
(‡ Signal Tower.)FIG.12.
FIG.12.
(‡ Signal Lamps.)FIG.13.
FIG.13.
As the trains when going at a considerable speed cannot be suddenly stopped, it is necessary to have signals placed in certain conspicuous positions, that the engine driver may begin to stop the train (when necessary) in time; this he effects by what is called a “break,” a contrivance by which two pieces of wood are made (by turning a screw) to grasp firmly each of a pair of wheels, and so prevent them turning round, this produces so much friction against the trams that (after the steam is turned off) the onward motion of the train is soon stopped. The signals are of three kinds generally, a red flag to indicate danger, a green one to caution, and a white one to show that the way is clear; these are (on most occasions) held by a man and waved to and fro to attract attention, but there are however a great many occasions for fixed signals, as at stations and bends in the line where the engine driver can only see a short distance ahead; these fixed signals consist of tall posts placed where they can be seen at a considerable distance. These posts have an arrangement at the top consisting of a lamp with a “bull’s-eye” or lens at each side pointing up and down the line, and a pair of arms capable of being let down into the post, raised at right angles with it, or into a position midway between the post and a right angle (as shown infigs. 11and12). One side of each arm is painted red, the other white, one arm serving for a signal up the line and the other down; attached to the joint of each arm, close to the post, are two iron frames each holding a piece of colored glass, one red the other green, and so arranged that when the arm is at right angles to the post, the red glass is before the lamp and when the arm is let half way down the green glass comes in front of the lamp (fig. 13), thus the same action serves both for day and night signals. When the arm showing the red side projects in a horizontal direction, it indicates (in the day) “danger,” and so does the red light at night; when the arm is let down half way, it shows that caution is required, and the green glass then before the lamp shows the same signal at night; when the arm is let quite down out of sight, it shows safety, and so does the white light of the lamp thus freed from both screens of colored glass.
(‡ Engine Whistle.)FIG.14.
FIG.14.
Each engine is provided with a whistle (fig. 14)blown by steam turned on from the boiler, which is used as a signal at any particular time, especially in tunnels or when there is a fog; there is also an arrangement by which each engine presses on a lever at the side of the tram as it passes, and causes a bell to ring at the station, to announce its approach, when about a quarter of a mile off. In some cases, as in foggy weather, when the usual signals cannot be seen, a packet of fulminating powder is placed on the rail, and this being exploded by the wheel of the engine as it passes over it, gives notice of its approach, &c. There are other signals, but these are the chief.
ELECTRIC TELEGRAPHS.(‡ Electric Telegraph.)The power of transmitting messages to any distance or place to which a wire can be carried, and in a space of time too small to be reckoned, is without doubt one of the most wonderful inventions ever carried out by men’s hands. Although the signals are carried from place to place with a rapidity almost incredible, yet the electric fluid travels at a certain, although marvellously rapid rate. It is thought that light and the electric fluid both travel at the same rate, namely, 192,000 miles in a second, and if so, a message might be sent round the world (were it possible to carry on a wire) thrice in that small space of time.(‡ Acid Battery Cell.)FIG.1.(‡ Battery Series.)FIG.2.(‡ Grounding Effect.)FIG.3.The construction of the electric telegraph is pretty much the same everywhere, only that modifications of the same agent are used in different countries, and different signals formed; but whether this agent or influence is obtained from magnetic or galvanic sources, the result is exactly the same. When a pair of metallic plates are immersed in a fluid which acts chemically more rapidly on the one than the other, and a wire connects the upper parts of these plates, this wonderful agency is set in motion, and circulates from the one plate to the other (fig. 1). This arrangement may be best shown by using one plate of zinc and the other of copper, and a dilute solution of sulphuric acid for the liquid; this, however, produces by far too little of the agent to be used on a telegraphic line, there are therefore combinations of such pairs of plates so arranged that the power of one pair shall be added to the next in such a way that at the end of the series (called a “battery”) there shall be a great increase of the power accumulated—this arrangement is shown infig. 2. Now (if the power be sufficient) it does not signify what length of wire there may be between the two ends of this arrangement or “battery,” whether the ends be connected by a few feet of wire, or as many hundred miles—the electricity passes instantaneously from one end to the other; and furthermore, it has been found in practice, that this electrical influence can be transmitted through the earth in one direction if sent by a wire in the other; for instance, if a wire from one end of the battery be carried on from London to Liverpool; instead of having another from Liverpool to London, to connect the two ends of the battery, it is found to answer the same purpose if the end of the wire at Liverpool be fastened to a plate of metal buried beneath the surface of the earth and the other end of the battery at London, furnished with a similar plate also buried. In this arrangement, the electricity will pass beneath the surface of the earth from Liverpool to London, and through the wire from London to Liverpool, thus completing the circuit. The end from which the electricity passes is called the “positive electrode,” that to which it returns the “negative electrode.”Fig. 3will show this arrangement.(‡ Electro-Magnet.)FIG.4.(‡ Electro-Magnet Turned On.)FIG.5.(‡ Angled View Of Electro-Magnet.)FIG.6.If a bar-magnet be suspended on a pivot so that it may turn freely, it will (as is well known) turn with one end to the north, which is owing to a current of natural electricity passing round the earth in the direction of east and west, the magnet crossing the current at a right angle; and if a coil of wire coated with silk (to keep one part of the coil from another) be placed round, above and below the long axis of a bar of steel as shown atfig. 4, and a current of electricity passed through this wire, the steel becomes a magnet and will take a direction similar to the natural magnet, more or less at right angles to this coil, as infig. 5, according to the intensity of the current; and the instant this electrical current is stopped it will resume its former direction. This fact has been made use of to form the principal feature of all English telegraphs; in the telegraph such a needle is mounted in an upright position, and instead of its tendency to turn to the north, a tendency to maintain the upright position is given to it by having one of the arms of the magnet a little heavier than the other; such a magnet having a coil of wire surrounding it. When the electric current passes through the coil, it will turn out of the upright position to either one side or the other, according to the direction of the current, from its tendency to assume a position at an angle to the current (fig. 6); if the current be stopped even for an instant, then the needle or magnet will again assume its upright position. The pivot of this magnet is brought forward and has on its front part another needle, which being on the same pivot turns with it; this is visible on the outside of the apparatus, and is looked at to ascertain the movement of the one within. There is also an arrangement called a “commutator,” so contrived, that by moving a handle to the right or left, a connection shall be made with either end of the battery, and thereby cause the direction of the current and needle to be changed at pleasure; also by moving the handle into an upright position the current shall be stopped; and finally, by a third movement, a bell shall be rung. Now, as has already been explained, when the current goes in one direction, the magnetic needle is deflected in that direction; and when the current is reversed the position of the needle is also reversed, and when the current is cut off the needle will resume its perpendicular position. If two such needles and two such handles be at each station, when the handles at one station are moved, the needles at the other station will take on a similar movement; and when the handles at that station are moved, the needles at the first station will be moved to correspond. This constitutes the system of communication kept up by the electric telegraphs in England; but it remains to be shown how all the letters of the alphabet, the numerals, &c., can be represented by the movements of the two handles.(‡ Eight Needle Positions.)FIG.7.(‡ Telegraph Poles.)FIG.8.(‡ Wire Insulator.)FIG.9.(‡ Six-Wire Cable.)FIG.10.These handles can be placed in eight positions (besides the upright one) by a single movement of each hand, as may be seen infig. 7; and these eight signals if repeated, or made twice in rapid succession will make eight more, and by being repeated three times will constitute a third eight, making twenty-four; finally, by a rapid motion right and left, they may be caused to signify a fourth eight, or thirty-two signals, which are found to be sufficient for every purpose, and by practice may be both produced and read off with facility. Before a message is about to be delivered the commutator is so placed as to ring a bell, which is done by the same arrangement as in a common alarm-clock, but the action is set in motion by a peculiar contrivance, which depends upon the property a bar of soft iron has of becoming magnetic when a wire is wound round it and a current of electricity passed through this wire; this magnetic property exists only as long as the current passes, and stops the instant it is cut off. The catch of the alarm is disengaged by the movement of a bar of iron being drawn to the magnet while the current passes, and forced back again by a spring when it is stopped, thus setting in action the mechanism of the alarm, or in some cases there is a simple contrivance for causing a rapid flow and stoppage of the electricity, so that the bar is alternately attracted by the magnet and released by the spring, and this motion of the bar rings the bell as long as it is continued. The bell is always rung to give notice that a message is about to be sent, and at the station where the bell rings, the bell at the former station is rung in return, to show that they are prepared to receive the message; the message is then spelt letter by letter, by moving the handles into the proper positions, and as the message is being sent, the eye is kept on the dials having the needles which will communicate any message in return from the station to which the message is being sent, such as “repeat,” “not understood,” &c., &c., for which certain single signs are made and recognised.The wires which convey the electricity from station to station, are made of galvanized iron (iron coated with zinc), and must be kept from all communication with the earth by some substance incapable of conducting it; they are therefore stretched between wooden poles (fig. 8), and rest upon sockets or supports of glass or glazed earthenware, which are both substances incapable of conducting the electricity to the earth (fig. 9). In certain localities, as in towns, the wires are coated with gutta percha (another non-conductor), and laid side by side in a tube under ground; this is also done in the longer tunnels. In the cables which conduct the electric power along the bottom of the sea as from Dover to Calais; the wires are first coated with gutta percha, then bound with yarn soaked in tar, and finally coated with galvanized iron wires wound round spirally like the strands of a rope (fig. 10), the whole forming a cable which is coiled up in the hold of a vessel, and let out as the vessel crosses from one side to the other; in this way the cable is deposited on the bed of the sea or channel, forming an electrical connection from country to country. These cables are made in one piece by machinery. That from Dover to Calais is twenty-five miles long, contains four copper conducting wires, and weighs about 175 tons; that from Dover to Ostend contains six conducting wires, is seventy miles long, weighs nearly 500 tons, and cost about £30,000; its structure (the real size) is shown atfig. 10.ELECTRIC TIME BALL, CHARING CROSS.The electric cable now constructed to be laid down between Ireland and America, is composed of seven small copper wires twisted into one, and surrounded by gutta percha; this is then surrounded by eighteen small wire-ropes, each composed of seven small wires twisted together, the whole being in its section not larger than a four-penny-piece; 2000 miles of this cable are now ready to be laid down. A plan was some time ago put in practice by which the correct time could be kept at various places by electric communication with the time at Greenwich; a clock thus regulated, is situated at Charing Cross, and a ball placed at the top of the electric telegraph station there, is caused by the same means to fall exactly at one o’clock. A contrivance has of late been patented to work the electric telegraph by steam, and the following account of it is extracted from the “Times:”—“A series of gutta percha bands, about six inches wide and a quarter of an inch thick, are coiled on wheels on drums arranged for the purpose. These bands are studded down both sides with a single row of holes at short intervals apart. When a message is to be sent the clerks wind off these bands, inserting in the holes small brass pins, which, according to their combinations in twos or threes (with blank holes between), represent certain words or letters. In this manner the message is, as it were, “set up” in the bands with great rapidity, and if the number of bands employed is sufficiently large—say as numerous as the compositors employed in a large printing-office—messages equal in length to five or six columns of this journal could be set up and ready for transmission in the course of a single hour. Of course this operation in no respect interferes with the telegraph wire itself, which continues free for use until the bands of messages are actually being despatched. The gutta percha bands when full are removed to the instrument-room, a most simple appliance preventing any derangement or falling out of the pins while being moved about. In the instrument-room the bands are connected with ordinary steam machinery, by which they are drawn in regular order with the utmost rapidity between the charged poles of an electrical machine in such a manner that, during the moment of each pin’s passing, it forms electrical communication between the instrument and the telegraph, and a signal is transmitted to the other end of the wire, where the spark perforates a paper and records the message. The only limit to the rapidity of the operation is the rate at which the bands can be drawn, since the electrical contact of each pin, even for the 200th part of a second, is more than sufficient to transmit a word or signal from London and register it in America. Of course, as the message is recorded (we will say in America) with the same rapidity as that with which it is transmitted from London, a number of reading clerks will be requisite in order to translate it, by dividing it into small portions, with almost as much facility as it has been sent.”
(‡ Electric Telegraph.)
The power of transmitting messages to any distance or place to which a wire can be carried, and in a space of time too small to be reckoned, is without doubt one of the most wonderful inventions ever carried out by men’s hands. Although the signals are carried from place to place with a rapidity almost incredible, yet the electric fluid travels at a certain, although marvellously rapid rate. It is thought that light and the electric fluid both travel at the same rate, namely, 192,000 miles in a second, and if so, a message might be sent round the world (were it possible to carry on a wire) thrice in that small space of time.
(‡ Acid Battery Cell.)FIG.1.
FIG.1.
(‡ Battery Series.)FIG.2.(‡ Grounding Effect.)FIG.3.
(‡ Battery Series.)FIG.2.
FIG.2.
(‡ Grounding Effect.)FIG.3.
FIG.3.
The construction of the electric telegraph is pretty much the same everywhere, only that modifications of the same agent are used in different countries, and different signals formed; but whether this agent or influence is obtained from magnetic or galvanic sources, the result is exactly the same. When a pair of metallic plates are immersed in a fluid which acts chemically more rapidly on the one than the other, and a wire connects the upper parts of these plates, this wonderful agency is set in motion, and circulates from the one plate to the other (fig. 1). This arrangement may be best shown by using one plate of zinc and the other of copper, and a dilute solution of sulphuric acid for the liquid; this, however, produces by far too little of the agent to be used on a telegraphic line, there are therefore combinations of such pairs of plates so arranged that the power of one pair shall be added to the next in such a way that at the end of the series (called a “battery”) there shall be a great increase of the power accumulated—this arrangement is shown infig. 2. Now (if the power be sufficient) it does not signify what length of wire there may be between the two ends of this arrangement or “battery,” whether the ends be connected by a few feet of wire, or as many hundred miles—the electricity passes instantaneously from one end to the other; and furthermore, it has been found in practice, that this electrical influence can be transmitted through the earth in one direction if sent by a wire in the other; for instance, if a wire from one end of the battery be carried on from London to Liverpool; instead of having another from Liverpool to London, to connect the two ends of the battery, it is found to answer the same purpose if the end of the wire at Liverpool be fastened to a plate of metal buried beneath the surface of the earth and the other end of the battery at London, furnished with a similar plate also buried. In this arrangement, the electricity will pass beneath the surface of the earth from Liverpool to London, and through the wire from London to Liverpool, thus completing the circuit. The end from which the electricity passes is called the “positive electrode,” that to which it returns the “negative electrode.”Fig. 3will show this arrangement.
(‡ Electro-Magnet.)FIG.4.(‡ Electro-Magnet Turned On.)FIG.5.(‡ Angled View Of Electro-Magnet.)FIG.6.
(‡ Electro-Magnet.)FIG.4.
FIG.4.
(‡ Electro-Magnet Turned On.)FIG.5.
FIG.5.
(‡ Angled View Of Electro-Magnet.)FIG.6.
FIG.6.
If a bar-magnet be suspended on a pivot so that it may turn freely, it will (as is well known) turn with one end to the north, which is owing to a current of natural electricity passing round the earth in the direction of east and west, the magnet crossing the current at a right angle; and if a coil of wire coated with silk (to keep one part of the coil from another) be placed round, above and below the long axis of a bar of steel as shown atfig. 4, and a current of electricity passed through this wire, the steel becomes a magnet and will take a direction similar to the natural magnet, more or less at right angles to this coil, as infig. 5, according to the intensity of the current; and the instant this electrical current is stopped it will resume its former direction. This fact has been made use of to form the principal feature of all English telegraphs; in the telegraph such a needle is mounted in an upright position, and instead of its tendency to turn to the north, a tendency to maintain the upright position is given to it by having one of the arms of the magnet a little heavier than the other; such a magnet having a coil of wire surrounding it. When the electric current passes through the coil, it will turn out of the upright position to either one side or the other, according to the direction of the current, from its tendency to assume a position at an angle to the current (fig. 6); if the current be stopped even for an instant, then the needle or magnet will again assume its upright position. The pivot of this magnet is brought forward and has on its front part another needle, which being on the same pivot turns with it; this is visible on the outside of the apparatus, and is looked at to ascertain the movement of the one within. There is also an arrangement called a “commutator,” so contrived, that by moving a handle to the right or left, a connection shall be made with either end of the battery, and thereby cause the direction of the current and needle to be changed at pleasure; also by moving the handle into an upright position the current shall be stopped; and finally, by a third movement, a bell shall be rung. Now, as has already been explained, when the current goes in one direction, the magnetic needle is deflected in that direction; and when the current is reversed the position of the needle is also reversed, and when the current is cut off the needle will resume its perpendicular position. If two such needles and two such handles be at each station, when the handles at one station are moved, the needles at the other station will take on a similar movement; and when the handles at that station are moved, the needles at the first station will be moved to correspond. This constitutes the system of communication kept up by the electric telegraphs in England; but it remains to be shown how all the letters of the alphabet, the numerals, &c., can be represented by the movements of the two handles.
(‡ Eight Needle Positions.)FIG.7.
FIG.7.
(‡ Telegraph Poles.)FIG.8.(‡ Wire Insulator.)FIG.9.(‡ Six-Wire Cable.)FIG.10.
(‡ Telegraph Poles.)FIG.8.
FIG.8.
(‡ Wire Insulator.)FIG.9.
FIG.9.
(‡ Six-Wire Cable.)FIG.10.
FIG.10.
These handles can be placed in eight positions (besides the upright one) by a single movement of each hand, as may be seen infig. 7; and these eight signals if repeated, or made twice in rapid succession will make eight more, and by being repeated three times will constitute a third eight, making twenty-four; finally, by a rapid motion right and left, they may be caused to signify a fourth eight, or thirty-two signals, which are found to be sufficient for every purpose, and by practice may be both produced and read off with facility. Before a message is about to be delivered the commutator is so placed as to ring a bell, which is done by the same arrangement as in a common alarm-clock, but the action is set in motion by a peculiar contrivance, which depends upon the property a bar of soft iron has of becoming magnetic when a wire is wound round it and a current of electricity passed through this wire; this magnetic property exists only as long as the current passes, and stops the instant it is cut off. The catch of the alarm is disengaged by the movement of a bar of iron being drawn to the magnet while the current passes, and forced back again by a spring when it is stopped, thus setting in action the mechanism of the alarm, or in some cases there is a simple contrivance for causing a rapid flow and stoppage of the electricity, so that the bar is alternately attracted by the magnet and released by the spring, and this motion of the bar rings the bell as long as it is continued. The bell is always rung to give notice that a message is about to be sent, and at the station where the bell rings, the bell at the former station is rung in return, to show that they are prepared to receive the message; the message is then spelt letter by letter, by moving the handles into the proper positions, and as the message is being sent, the eye is kept on the dials having the needles which will communicate any message in return from the station to which the message is being sent, such as “repeat,” “not understood,” &c., &c., for which certain single signs are made and recognised.The wires which convey the electricity from station to station, are made of galvanized iron (iron coated with zinc), and must be kept from all communication with the earth by some substance incapable of conducting it; they are therefore stretched between wooden poles (fig. 8), and rest upon sockets or supports of glass or glazed earthenware, which are both substances incapable of conducting the electricity to the earth (fig. 9). In certain localities, as in towns, the wires are coated with gutta percha (another non-conductor), and laid side by side in a tube under ground; this is also done in the longer tunnels. In the cables which conduct the electric power along the bottom of the sea as from Dover to Calais; the wires are first coated with gutta percha, then bound with yarn soaked in tar, and finally coated with galvanized iron wires wound round spirally like the strands of a rope (fig. 10), the whole forming a cable which is coiled up in the hold of a vessel, and let out as the vessel crosses from one side to the other; in this way the cable is deposited on the bed of the sea or channel, forming an electrical connection from country to country. These cables are made in one piece by machinery. That from Dover to Calais is twenty-five miles long, contains four copper conducting wires, and weighs about 175 tons; that from Dover to Ostend contains six conducting wires, is seventy miles long, weighs nearly 500 tons, and cost about £30,000; its structure (the real size) is shown atfig. 10.
ELECTRIC TIME BALL, CHARING CROSS.
ELECTRIC TIME BALL, CHARING CROSS.
The electric cable now constructed to be laid down between Ireland and America, is composed of seven small copper wires twisted into one, and surrounded by gutta percha; this is then surrounded by eighteen small wire-ropes, each composed of seven small wires twisted together, the whole being in its section not larger than a four-penny-piece; 2000 miles of this cable are now ready to be laid down. A plan was some time ago put in practice by which the correct time could be kept at various places by electric communication with the time at Greenwich; a clock thus regulated, is situated at Charing Cross, and a ball placed at the top of the electric telegraph station there, is caused by the same means to fall exactly at one o’clock. A contrivance has of late been patented to work the electric telegraph by steam, and the following account of it is extracted from the “Times:”—
“A series of gutta percha bands, about six inches wide and a quarter of an inch thick, are coiled on wheels on drums arranged for the purpose. These bands are studded down both sides with a single row of holes at short intervals apart. When a message is to be sent the clerks wind off these bands, inserting in the holes small brass pins, which, according to their combinations in twos or threes (with blank holes between), represent certain words or letters. In this manner the message is, as it were, “set up” in the bands with great rapidity, and if the number of bands employed is sufficiently large—say as numerous as the compositors employed in a large printing-office—messages equal in length to five or six columns of this journal could be set up and ready for transmission in the course of a single hour. Of course this operation in no respect interferes with the telegraph wire itself, which continues free for use until the bands of messages are actually being despatched. The gutta percha bands when full are removed to the instrument-room, a most simple appliance preventing any derangement or falling out of the pins while being moved about. In the instrument-room the bands are connected with ordinary steam machinery, by which they are drawn in regular order with the utmost rapidity between the charged poles of an electrical machine in such a manner that, during the moment of each pin’s passing, it forms electrical communication between the instrument and the telegraph, and a signal is transmitted to the other end of the wire, where the spark perforates a paper and records the message. The only limit to the rapidity of the operation is the rate at which the bands can be drawn, since the electrical contact of each pin, even for the 200th part of a second, is more than sufficient to transmit a word or signal from London and register it in America. Of course, as the message is recorded (we will say in America) with the same rapidity as that with which it is transmitted from London, a number of reading clerks will be requisite in order to translate it, by dividing it into small portions, with almost as much facility as it has been sent.”