CHAPTER XIX.

Fig. 233.Fig. 233.

Boy,evidently shocked, behind doctor's carriage provided with a small coil machine.

The correlation of the physical forces, heat, light, electricity, magnetism, and motion, is one of the most interesting subjects for study that can be suggested to the lover of science. The examination of the precise meaning of the term correlation, so ably considered by Professor Grove, indicates a necessary mutual or reciprocal dependence of one force on the other. Thus, electricity will produce heat, andvice versÃ¢; motion, such as friction, produces electricity, and the latter, by its attraction and repulsion, establishes itself as a source of motion. Electricity produces light, also magnetism, and contrariwise light is said to possessthe power of magnetizing steel, whilst magnetism again produces light and electricity. Such are the intimate connexions that exist between these imponderable agents, and we may trace cause and effect and its reversal amongst these forces, until the mind is lost in the examination of the bewildering mazes, and is content to return to the beaten track and work out experimentally the practical truths. We have had occasion to notice in another part of this playbook the fact that a current of electricity causes the evolution of magnetism in its passage through various conducting media, and the truth has been specially illustrated by the various experiments in the chapter devoted to electro-magnetism. In commencing this portion of electrical science, we have no new terms to coin for the title of the discourse, as we merely reverse the other when we examine the nature and peculiarities of

Fig. 234.Fig. 234.

Clarke's magneto-electrical machine.

The source of the power must necessarily be a bar or horse-shoe shaped piece of steel permanently endowed with magnetism. If the former is thrust into a cylinder of wood or pasteboard, around which coils of covered copper wire have been carefully wound, so that the extremities communicate with a galvanometer, an immediate deflection of the needle occurs, which, however, quickly returns to its first position, but is again deflected in the opposite direction on the withdrawal of the steel magnet from the coil of copper wire. (Fig. 235.)

Fig. 235.Fig. 235.

a b.Coil of copper wire.c.Permanent bar magnet placed inside the coil, when the galvanometer needle,d, is deflected.

The rapid entrance and exit of the steel magnet in the helix of copper wire would be insufficient to produce any quantity of electricity, and the ingenuity of man has been taxed to arrange a method by which a magnet may be suddenly formed and destroyed inside a coil of insulated copper wire. The difficulty, however, has been surmounted by several ingenious contrivances, based on the principles first discovered by Faraday; and the one especially to be noticed is the revolution of a coil of copper wire enclosing a piece of soft iron, called thearmature, before the poles of a powerful magnet. The first machine was inventedby M. Hypolyte Pixii, of Paris, and in 1833, Mr. Saxton improved upon this machine, and three years afterwards, Mr. E. M. Clarke described a very ingenious modification of the electro-magnetic machine, which is depicted below. In this picture, the letterais the permanent fixed horse-shoe magnets, which are very appropriately termed thebatterymagnets, because they take the position that would otherwise be occupied by a voltaic battery, and they are indeed the prime source of the electrical power that is evoked.dis the intensityarmaturewhich screws into a brass mandril seated between the poles of the magnetsa, motion being communicated to it by the multiplying wheel,e. This armature orinductorhas two coils of fine insulated copper wire of 1500 yards in length, coiled on its cylinders, the commencement of each coil being soldered to the bard, from which projects a brass stem, also soldered intod, carrying the break-pieceh, which is made fast in any position by a small binding-screw in a hollow brass cylinder to which the other terminations of the coils,f f, are soldered, these being insulated by a piece of hard wood attached to the brass stem.ois an iron wire spring pressing against one end of the hollow brass cylinder;pis a square brass pillar;qis a metal spring that rubs gently on the break-pieceh;tis a copper wire for connecting the brass pieces with the woodlbetween them, and out of whichpandopass;r rare two handles of brass with metallic wires, the end of one being inserted into either of the brass pieces connected withpando, and the other into the brass stem that carries the break-pieceh, delivers a most severe shock directly the wheel is set in motion.

In Saxton's electro-magnetic machine, the permanent steel magnets are placed horizontally instead of perpendicularly, and are composed of six or more horse-shoe-shaped pieces of steel. The armatures, or inductors, or electro-magnets (for they consist of pieces of soft round iron with wire wound round them), are two in number, and are adapted to exhibit eitherquantityorintensityeffects. The quantity armature is constructed of stout iron, and covered with thick insulating wire. The intensity armature is made of slighter iron, and covered with from one thousand to two thousand yards of fine copper wire coated with silk. Thequantityarmature is intended for the exhibition of results similar to those which are procurable from a voltaic battery, such as the magnetic spark, inducing magnetism in soft iron, heating platinum wire. The intensity armature is employed for the chemical decomposition of water and other bodies, and likewise for the administration of those terrible blows to the nervous system which cause strong men of the mildest deportment to become painfully excited, and to make those ejaculations which are so peculiar to the genus John Bull.

EXPERIMENTS WITH THE MAGNETO-ELECTRIC MACHINE.

The decomposition of water by the passage of electricity from one platinum plate to another, has already been illustrated atpage 198. Thesame fact may likewise be displayed by the following arrangement of the machine. (Fig. 236.)

Fig. 236.Fig. 236.

a.Apparatus for decomposing water and collecting the gases separately.b b.Wires proceeding from the machine atm,n.q, works on the single break,h.

The electric light obtained by the passage of the electricity from the battery through the charcoal points, is also an effect that can be produced by magneto-electric machines, the wires leading from the pointsa bbeing insulated by glass handles, and placed in the holesm n. (Fig. 237.)

Fig. 237.Fig. 237.

The electric light obtained from the magneto machine.

The scintillation of iron wire is one of the most pleasing experiments with this apparatus, and is performed by pressing gently one end of a piece of thin iron wire (attached by means of a binding-screw to the upright bara) against the armature,d. (Fig. 238.)

Fig. 238.Fig. 238.

Deflagration of iron wire.

The combustion of ether or other inflammable spirit may also be demonstrated with the aid of this powerful apparatus, and the arrangement, in common with the others employed by Mr. Clarke, is shown in Fig. 239.

Fig. 239.Fig. 239.

The break is removed, and the double blades,b, fixed in its place. The brass cup,a, containing mercury is so adjusted that the points will leave the surface of the mercury when the armature is vertical. Ether or alcohol poured on the surface is quickly inflamed by the electric spark.

With the assistance of the magneto-electric machine, telegraphic communication may be conducted without the assistance of a battery. It has also been applied to the art of electro-plating by Mr. J. P. Woolrich, of Birmingham; and whilst visiting that place, the author had the opportunity of witnessing the arrangement employed.

It consists of a very powerful magneto-electric machine turned by a steam-engine, and connected with the large troughs containing the silvering solution. If it is required to deposit a thin coating of silver on the article, a short period suffices for the action of the machine, whilst a thick deposit of the precious metal is only obtained by the constant operation of the magnets for several hours. At Mr. Woolrich's factory, the goods which were being coated with silver were all kept in motion, moving slowly backwards and forwards in the trough by means of an eccentric connectedwith the same steam-engine that worked the electro-magnetic machine. (Fig. 240.)

Fig. 240.Fig. 240.

Silvering and plating by the magneto machine, turned by a steam-engine.

The magneto-electric telegraph patented by Mr. Henley in 1848, offers another example of the application of the electric current induced in electro-magnetic coils, when they rotate in close proximity to the poles of a powerful steel magnet. This telegraph is now in constant use by the English and Irish Magnetic Telegraph Company, through a distance of more than 2100 miles. The whole length of wires in use amounts to the astonishing quantity of 13,900 miles, of which 6350 miles are hidden underground, and 7500 conducted above.

This telegraph is considered to be one of the simplest and most economical yet brought into practical working.

At the end of the chapter devoted to the subject of light, will be found an experiment devised and carried out by Dr. Faraday, in which it is shown that if a bar of a peculiar glass (called after the inventor,Faraday's heavy glass, or silicated borate of lead) is subjected to the inductive action of a very powerful electro-magnet, that it has the power of changing the direction of a ray of polarized light transmitted through it. This effect is not confined to the poles of an electro-magnet, but is also perceptible (though in a diminished degree) with ordinary magnets.

The result of this important experiment was communicated to the Royal Society by Dr. Faraday on the 27th November, 1845, the enunciation of the fact by this learned philosopher being, "that when 'the line of magnetic force' is made to pass through certain transparent bodies parallel to a ray of polarized light traversing the same body, the ray of polarized light experiences a rotation." Now, "the line of magnetic force" means that continual flow of the magnetic current which passes from pole to pole, and is indicated by iron filings sprinkled on paper placed above the poles of a magnet, and usually termedmagnetic curves, or the curved lines of magnetic force. (Fig. 241.)

Fig. 241.Fig. 241.

The curved lines of magnetic force.

The heavy glass already alluded to, upon which the magnet exerts a certain influence, is called

and by this term is meant a body through which the lines of magnetic force are passing without affecting it like iron or steel. Atpage 211is a picture representing (at Figs. 201 and 202) the direction of the electricity and that of the magnetic current or whirl at right angles to it. If, then, Fig. 202 be considered as a piece of glass, the arrowa bwill show "the line of magnetic force," the pointbbeing the north pole, and the shaftathe south pole of the magnet, and the arrows traced round will represent direction. This simple drawing expresses the whole of the law of the action of the magnet on the glass, and if kept in view, will give every position and consequence of direction resulting from it.

The phenomenon of the affection of the beam of polarized light is immediately connected with the magnetic force, and this is supposed to be proved by thebrightnessof the polarized ray being developedgradually, as the iron coiled with wire requires about two seconds to acquire its greatest power after being connected with the battery.

In another experiment of Faraday's, where a beam of polarized light was sent through a long glass tube containing water, and introduced as a coreinsidea powerful electro-magnetic coil, the image of a candle viewed with a proper eye-piece, appeared or disappeared as the battery connexion was made or broken with the coil; but this result is not considered by many philosophers to be conclusive of the action of magnetism on light, but rather as an alteration of therefractingpower of the medium through which the light passes. These experiments were the precursors of the other effects of magnetism upon different kinds of matter which Faraday discovered, and he commenced his examination with a small bar of heavy glass suspended by a filament of silk between the poles of an electro-magnet, and when the twisting or effects of torsion had ceased, the battery was connected. Directly the current passed, Faraday's keen eye detected a movement of the glass, and on repeating the experiment, he discovered that the movement was not accidental, but always took place in a certain fixed directionâ€”viz., a direction at right angles to a line drawn across and touching the two poles of a horse-shoe-shaped magnetâ€”i.e., supposing the feeder or bit of soft iron usually placed in contact with the poles of the horse-shoe-magnet to represent the "axial line," any line drawn across it at right angles would be called theequatorial line, whilst the general space included between the poles of the magnet is called "themagnetic field." The movement of the heavy glass was thereforeequatorial, and it pointed east and west instead of north and south, like iron and steel.

Fig. 242.Fig. 242.

A cube of copper suspended between the poles of a powerful electro-magnet.

By the use of the apparatus (Fig. 242) Faraday proved that everysubstance, whether solid, fluid, or gaseous, was subject to magnetic influences, assuming either the axial or equatorial position. The apparatus consists of a prolongation of the poles of a powerful electro-magnet, between whichthecube of copper, weighing from a quarter to half a pound, suspended by a thread, may be set spinning or rotating. If the electro-magnet is connected with the battery, the cube stops immediately, and whilst still in the same position or in themagnetic field, with the magnet in full action, it is impossible to set it spinning or twisting round again. (Fig. 242.)

A large number of other substances, solid, liquid, and gaseous, were submitted to the action of the magnet, the liquids and gases being hermetically sealed in glass tubes, and some of the results are detailed in the following list:

Bodies that point axially, or are paramagnetic, like a suspended needle.

Iron.Nickel.Cobalt.Manganese.Chromium.Cerium.Titanium.Palladium.Platinum.Osmium.Paper.Sealing-wax.Fluor spar.Peroxide of lead.Plumbago.China ink.Berlin Porcelain.Red-lead.Sulphate of zinc.Shell-lac.Silkworm-gut.Asbestos.Vermilion.Tourmaline.Charcoal.All salts of iron,when the latter is basic.Oxide of titanium.Oxide of chromium.Chromic acid.Salts of manganese.Salts of chromium.Oxygen, which standsalone as a paramagnetic gas.

Bodies that point equatorially, or are diamagnetic, like Faraday's heavy glass.

Bismuth.Antimony.Zinc.Tin.Cadmium.Sodium.Mercury.Lead.Silver.Copper.Gold.Arsenic.Uranium.Rhodium.Iridium.Tungsten.Rock crystal.The mineral acids.Alum.Glass.Litharge.Common salt.Nitre.Phosphorus.Sulphur.Resin.Spermaceti.Iceland spar.Tartaric acid.Citric acid.Water.Alcohol.Ether.Sugar.Starch.Gum-arabic.Wood.Ivory.Dried mutton.Fresh beef.Dried beef.Apple.Bread.Leather.Fresh blood.Dried blood.Caoutchouc.Jet.Turpentine.Olive oil.Hydrogen.Carbonic acid.Carbonic oxide.Nitrous oxide (moderately).Nitric oxide (very slightly).Olefiant gas.Coal gas.

Nitrogen is neither paramagnetic nor diamagnetic, and is equivalent to a vacuum. Magnetically considered, it is like space itself, which may be considered as zero.

The termmagneticFaraday proposes should be a general one, like that ofelectricity, and includeallthe phenomena and effects produced by the power, and he proposes that bodies magnetic in the sense of iron should be calledparamagnetic, so that the division would stand thus:

Magnetic.........{ Paramagnetic,{ Diamagnetic;

All space above and within the limits of our atmosphere may be regarded as traversed by lines of force, and amongst others are the lines of magnetic force which affect bodies, as shown in the table of paramagnetic and diamagnetic bodies, which have the same relation to each other as positive and negative, or north and south, in electricity and magnetism.

The lines of magnetic force are assumed to traverse void space without change; but when they come in contact with matter of any kind they are either concentrated upon it or scattered according to the nature of the matter.

The power which urges bodies to the axial or equatorial lines is not a central force, but a force differing in character in the axial or radial directions. If a liquid paramagnetic body were introduced into the field of force, it would dilate axially, and form a prolate spheroid like a lemon, while a liquid diamagnetic body would dilate equatorially, and form an oblate spheroid like an orange. PlÃ¼cker has demonstrated that if magnetic solutions are placed in watch glasses across the poles of theelectro-magnet, they are heaped up in a very curious manner. The poles of the electro-magnet are pieces of soft iron, which may be drawn away or approached at pleasure, and according as the poles are nearer or further asunder, the magnetic liquids, such as solution of iron, are heaped up in one or two directions, as shown atbandcin Fig. 243.

Fig. 243.Fig. 243.

Glass dish holding magnetic solution of iron, and placed in the magnetic field.

"The diamagnetic power, doubtless," says Faraday, "has its appointed office, and one which relates to the whole mass of the globe. For though the amount of the power appears to be feeble, yet, when it is considered that the crust of the earth is composed of substances of which by far the greater portion belongs to the diamagnetic class, it must not be too hastily assumed that their effect is entirely overruled by the action of the magnetic matters, whilst the great mass of waters and the atmosphere must exert their diamagnetic action uncontrolled."

PlÃ¼cker has also announcedâ€”what at the time he believed to be trueâ€”the highly interesting and important fact that the optic axis of Iceland or calcareous spar is repelled by the magnet and placed equatoriallyâ€”a fact which PlÃ¼cker thought true of many other crystals when the magnetic axis is parallel to the longer crystallographic axis. A piece of kyanite, which is a mineral composed of sand, clay, often lime, iron, water, and is used in India, being cut and polished as a gem, and sold frequently as an inferior kind of sapphire, will, it is said, even under the influence of the earth's magnetism, arrange itself like a magnetic needle.

PlÃ¼cker believed that he had discovered an existing relation between the forms of the ultimate particles of matter and the magnetic forces, and he imagined that the results he obtained would lead gradually to the determination of crystalline form by the magnet. The experiments of Tyndal and Knoblauch lead, however, to a very opposite series of conclusions, and by ingeniously powdering the crystals with water, and making them into a paste, which was afterwards dried and suspendedas a model in "the magnetic field;" also by taking a slice of apple about as thick as a penny-piece, with some bits of iron wire through it, in a direction perpendicular to its flat surface, they were found to set equatorially not by repulsion but by the attraction of the iron wires; or instead of the iron by placing bismuth wires, the apple now settled axially, not by attraction but by the repulsion of the bismuth. Ipecacuanha lozenges, Carlisle biscuits also, suspended in the magnetic field, exhibited a most striking directive action. The materials in these two cases werediamagnetic; but owing to the pressure exerted in their formation their largest horizontal dimensions set from pole to pole, the line of compression being equatorial; and it is a universal law "that in diamagnetic bodies the line along which the density of the mass has been induced by compression sets equatorial, and in magnetic bodies axial." Hence they assume, from these and many other conclusive experiments, that crystallized bodies, such as Iceland spar, take their position in the magnetic field without reference to the existence of an "optic axis."

At the conclusion of a brilliant lecture at the Royal Institution by Dr. Tyndal "On the influence of material aggregation upon the manifestations of force," in which PlÃ¼cker's experiments respecting the repulsion of the optic axis were gracefully discussed and his theory refuted, the learned doctor said: "This evening's discourse is in some measure connected with this locality; and thinking thus, I am led to inquire wherein the true value of a scientific discovery consists? Not in its immediate results alone, but in the prospect which it opens to intellectual activityâ€”in the hopes which it excitesâ€”in the vigour which it awakens. The discovery which led to the results brought before us to-night was of this character.Thatmagnet[E]was the physical birthplace of these results; and if they possess any value they are to be regarded as the returning crumbs of that bread which in 1846 was cast so liberally upon the waters. I rejoice, ladies and gentlemen, in the opportunity here afforded me of offering my tribute to thegreatest workmanof the age, and of laying some of the blossoms of that prolific tree which he planted at the feet of the great discoverer of diamagnetism."[F]

[E]Alluding to a splendid magnet made by Logeman, which was sent to the Exhibition in Hyde-park in 1851. It could sustain a weight of 430 pounds, and was purchased by the Royal Institution for Dr. Faraday.

[F]Dr. Faraday.

It was first observed by Father Bancalari, of Genoa, that when the flame of a candle is placed between the poles of a magnet it is strongly repelled. The flames of combustible gases from various sources are differently affected, both by the nature of the combustible and by the nearness of the poles. Faraday repeated Bancalari's experiments, and by a certain arrangement of the poles of this magnet he obtained a powerful effect in themagnetic field, and having the axial line of the magnetic force horizontal, he found that when the flame of a wax taper was held near the axial line (but on one side or the other), and about one-third of the flame rising above the level of the upper surface of thepoles, as soon as the magnetic force was exerted the flame receded from the axial line, moving equatorially until it took an inclined position, as if a gentle wind was causing its deflection from the upright position.

When the flame was placed so as to rise truly across the magnetic axis, the effect of the magnetism was very curious, and is shown ata, Fig. 244.

On raising the flame a little more the effect of the magnetic force was to intensify the results already mentioned, and the flame actually became of afish-tailed shape, as atc, Fig. 244; and when the flame was raised until about two-thirds of it were above the level of the axial line, and the poles approached very close, the flame no longer rose between the poles, but spread out right and left on each side of the axial line, producing a double flame with two long tongues, as atb, Fig. 244.

Fig. 244.Fig. 244.

Effect of magnetism on candle-flame between the poles of the magnet.

It was these experiments that led to the important discovery of the paramagnetic property of oxygen, and proved in a decided manner that gaseous bodies when heated became more highly diamagnetic. Oxygen, which (tried in the air) is powerfully magnetic, becomes diamagnetic when heated. A coil of platinum wire heated by a voltaic current, and placed beneath the poles of Faraday's apparatus, occasioned a strong upward current of air; but directly the magnetic action commences the ascending current divides, and a descending current flows downbetweenthe upward currents.

The discovery, says Silliman, of the highly paramagnetic character of oxygen gas, and of the neutral character of nitrogen, the two constituents of air, is justly esteemed a fact of great importance in studying the phenomena of terrestrial magnetism. We thus see that one-fifth of the air by volume consists of an element of eminent magnetic capacity, after the manner of iron, and liable to great physical changes of density, temperature, &c., and entirely independent of the solid earth. In this medium hang the magnetic needles used as tests, and as this magnetic medium is daily heated and cooled by the sun's rays, its power oftransmitting the lines of magnetic force is then affected, influencing undoubtedly the diurnal changes of the magnetic needle.

For a complete digest of Faraday's discoveries in diamagnetism the reader is referred to the second edition of Dr. Noad's comprehensive and learned work entitled "A Manual of Electricity."

Coming always from the highest walks of philosophy to lower and "common things" one cannot help being reminded of the old-fashioned method ofdrawing upa sluggish fire, and the natural query is suggested whether the poker is to be considered as a weak magnet, and does influence and draw towards the fire a greater supply of magnetic oxygen gas? (Fig. 245.)

Fig. 245.Fig. 245.

interior of the optical box

The interior of the optical box at the Polytechnicâ€”looking towards the screen. The assistants are supposed to be showing the dissolving views.

Fig. 246.Fig. 246.

"The moon shines bright:â€”In such a night as this."â€”The Merchant of Venice.

"To gild refined gold, to paint the lily,To throw a perfume on the violet,To smooth the ice, or add another hueUnto the rainbow, or with taper lightTo seek the beauteous eye of heaven to garnish,Is wasteful and ridiculous excess."

Perfection admits of no addition, and it is just this feeling that might check the most eloquent speaker or brilliant writer who attempted to offer in appropriate language, the praises due to that first great creation of the Almighty, when the Spirit of God moved upon the face of the waters and said, "Let there be light." If any poet might be permitted to laud and glorify this transcendant gift, it should be the inspired Milton; who having enjoyed the blessing of light, and witnessed the varied and beautiful phenomena that accompany it, could, when afflicted by blindness, speak rapturously of its creation, in those sublime strains beginning withâ€”

"'Let there be light,' said God, and forthwith lightEthereal, first of things, quintessence pure,Sprung from the deep: and from her native eastTo journey through the airy gloom began,Sphered in a radiant cloud, for yet the sunWas not; she in a cloudy tabernacleSojourn'd the while. God saw the light was good,And light from darkness by the hemisphereDivided: light the day, and darkness night,He named."

There cannot be a more glorious theme for the poet, than the vast utility of light, or a more sublime spectacle, than the varied and beautiful phenomena that accompany it. Ever since the divine command went forth, has the sun continued to shine, and to remain, "till time shall be no more," the great source of light to the world, to be the means of disclosing to the eye of man all the beautiful and varied hues of the organic and inorganic world. By the help of light we enjoy the prismatic colours of the rainbow, the lovely and ever changing and ever varied tints of the forest trees, the flowers, the birds, and the insects; the different forms of the clouds, the lovely blue sky, the refreshing green fields; or even the graceful adornment of "the fair," their beautiful dresses of exquisite patterns and colours. Light works insensibly, and at all seasons, in promoting marvellous chemical changes, and is now fairly engaged and used for man's industrial purposes, in the pleasing art of photography; just as heat, electricity, and magnetism, (all imponderable and invisible agents,) are employed usefully in other ways.

The sources from whence light is derived are six in number. The first is the sun, overwhelming us with its size, and destroying life, sometimes, with his intense heat and light, when the piercing rays are not obstructed by the friendly clouds and vapours, which temper and mitigate their intensity, and prevent the too frequent recurrence of that quick and dire enemy to man, thecoup de soleil.

The body of the sun is supposed to be a habitable globe like our own, and the heat and light are possibly thrown out from one of the atmospheric strata surrounding it. There are probably three of these strata, the one believed to envelope the body of the sun, and to be directly in contact with it, is called thecloudy stratum; next to, and above this, is the luminous stratum, and this is supposed to be the source of heat and light; the third and last envelope is of a transparent gaseous nature. These ideas have originated from astronomers who have carefully watched the sun and discovered the presence of certain black spots calledMaculÃ¦, which vary in diameter from a few hundreds of miles to 40 or 50,000 miles and upwards. There is also a greyish shade surrounding the black spots called thePenumbra, and likewise other spots of a more luminous character termedFaculÃ¦; indeed the whole disc of the sun has a mottled appearance, and is stippled over with minute shady dots. The cause of this is explained by supposing that these various spots represent openings or breaks in the atmospheric strata, through which the black body of the sun is apparent or other portions of the three strata, just as if a black ball was covered with red, then with yellow, and finally with blue silk: on cutting through the blue the yellow is apparent; by snipping out pieces of the blue and yellow, the red becomes visible; and by slicing away a portion of the three silk coverings the black ball at last comes into view. On a similar principle it issupposed that the variety of spots and eruptions on the sun's face or disc may be explained. The evolution of light is not, however, confined to the sun, and it emanates freely from terrestrial matter by mechanical action, either by friction, or in some cases by mere percussion. Thus the axles of railway carriages soon become red hot by friction if the oil holes are stopped up; indeed hot axles are very frequent in railway travelling, and when this happens, a strong smell of burning oil is apparent, and flames come out of the axle box. The knife-grinder offers a familiar example of the production of light by the attrition of iron or steel against his dry grindstone.

The same result on a much grander scale is produced by the apparatus invented by the late Jacob Perkins; the combustion of steel ensues under the action, viz., the friction of a soft iron disc revolving with great velocity against a file or other convenient piece of hardened steel. (Fig. 247)

Fig. 247.Fig. 247.

Instrument for the combustion of steel.

The stand has a disc of soft iron fixed upon an axis, which revolves on two anti-friction wheels of brass. The disc, by means of a belt worked over a wheel immediately below it, is made to perform 5000 revolutions per minute. If the hardest file is pressed against the edge of the revolving disc, the velocity of the latter produces sufficient heat by the great friction to melt that portion of the file which is brought in contact with it, whilst some particles of the file are torn away with violence, and beingprojected into the air, burn with that beautiful effect so peculiar to steel. If the experiment is performed in a darkened room, the periphery of the revolving disc will be observed to have attained a luminous red heat. Thirty years ago every house was provided with a "tinder-box" and matches to "strike a light." Since the advent of prometheans and lucifers, the flint and steel, the tinder, and the matches dipped in sulphur, have all disappeared, and now the box might be deposited in any antiquarian museum under the portrait of Guy Fawkes, and labelled, "an instrument for procuring a light, extensively used in the early part of the nineteenth century." (Fig. 248.)

Fig. 248.Fig. 248.

c.The steel.b.The flint.e.The tinder.d.The matches of the old-fashioned tinder-box,a.

The rubbing of a piece of wood (hardened by fire, and cut to a point) against another and softer kind, has been used from time immemorial by savage nations to evoke heat and light; the wood is revolved in the fashion of a drill with unerring dexterity by the hands of the savage, and being surrounded with light chips, and gently aided by the breath, the latent fire is by great and incessant labour at last procured. How favourably the modern lucifers compare with these laborious efforts of barbarous tribes! a child may now procure a light with a chemically prepared metal, and great merit is due to that person who first devised a method of mixing together phosphorus and chlorate of potash and soadjusted these dangerous materials that they are as safe as the "old tinder-box," and have now become one of our domestic necessaries. Ignition, or the increase of heat in a solid body, is another source of light, and is well illustrated in the production of illuminating power from the combustion of tallow, oil, wax, camphine or coal gas. The termignitionis derived from the Latin (ignis, fire), and is quite distinct, and has a totally different meaning from that ofcombustion. If a glass jar is filled with carbonic acid gas, and a little tray placed in it containing some gun cotton, it will be found impossible to fire the latter with a lighted taper,i.e.by combustion (comburo, to burn), because the gas extinguishes flame which is dependent on a supply of oxygen; whereas if a copper or other metallic wire is made red hot or ignited, the carbonic acid has no effect upon the heat, and the red hot wire being passed through the gas, the gun cotton is immediately fired.

Flame consists of three partsâ€”viz., of an outer film, which comes directly in contact with the air, and has little or no luminosity; also of a second film, where carbon is deposited, and, first byignition, and finally by combustion, produces the light; and thirdly, of an interior space containing unburnt gas, which is, as it were, waiting its turn to reach the external air, and to be consumed in the ordinary manner. (Fig. 249.)

Back to Index Next