MISCELLANEOUSINTELLIGENCE.I.MECHANICALSCIENCE.◊1.On the combined Action of a Current of Air and the Pressure of the Atmosphere.—The phenomena observed by M. Clement Désormes34, when a flat plate is opposed to air or vapour passing into the atmosphere from an aperture in a plane surface, have been rendered so easy of production by M. Hachette, as to be at the command of any person in any situation. M. Hachette has also accompanied the description of his instruments with elucidations, experiments, and philosophical reasonings.The first simplification by M. Hachette was to make the nozzle of a pair of double chamber-bellows terminate in the middle of a flat plate; he found that when the bellows were worked, effects were produced opposite the jet of air of the kind described by M. Clement, disks of card and other substances being drawn towards the aperture against the direction of the current. At the same time that he described this experiment, he also announced his having produced the same effects by using a stream of water instead of a stream of air.Fig.1.Fig.2.The apparatus was still further simplified, so as to make the stream of air from the mouth sufficient to produce the effect. A tin tube, A,Fig.1, was soldered to the middle of a round tin plate, in the centre of which was a small orifice, E; three or four small projections of the tin,f f, were left at the edges of the plate, to prevent the disks of paper, card, or metal, from slipping off sideways. The figure is on a scale of one-half. Instead of the tin plate, a piece[p194]of smooth cork may be used, and for the tin tube, a glass tube, or one made by rolling up a piece of paper.If the tube be held horizontally, or inclining a little upward, and a disk of card or paper be placed loosely against the aperture in the plate, it will be found that, on applying the mouth to the end of the tube, and blowing air through, that the disk will not be driven away, but actually made to apply closely to the surface of the plate; and if turned towards the ground it will be found to remain opposite the hole, and not to fall until the current of air is stopped. Even a plate of tin may in this way be suspended by a current of air; which at first would be supposed to conjoin with gravity in forcing it to the ground. When the disk is flexible and slightly elastic, a heavy sound, and sometimes even a shrill tone, is produced by the vibrations of the plate.In explanation of this experiment, M. Hachette says, “The air is pushed from the mouth A of the tube, towards the orifice E of the plate; it strikes the part of the disk opposed to this orifice, and the mean pressure on that part is greater than the pressure of the atmosphere. The blown air then takes place of that between the plate and the disk opposed to it; it moves in this interval with a velocity decreasing from the edges of the aperture: the elastic force of this air decreases at the same time, so that its mean pressure between the plate and the inner face of the disk becomes less than the atmospheric pressure; and as this last pressure is exerted on the whole external face of the disk H, I, this disk, subject at the same time to the two contrary pressures on its opposing faces, obeys the greater, and is pushed towards the plate C D.”“It is not necessary that the disk, C D, should be near the orifice E, of the tube A E. LetFig.2 be an instrument composed of a hollow cylinder, C D F G, and a flat border of the dimensions C″ F, or G D″. Let a tube, A E, be fixed to the bottom of the cylinder, the orifice E having a diameter of about three millimeters (0.12 of inch). If air be blown in at A, against the disk, H I, in the neighbourhood of the flat border, the disk will be urged towards the orifice E. This instrument is also delineated on a scale of one half. The disk, with the attached weight, weighs about 12 grammes (184.87 grains), being 54 millimeters in diameter; the pressure of the atmosphere upon it equals 23 kilogrammes: from which it follows that, in this experiment, the pressure of the air blown upon the inner surface of the disk, and the atmospheric pressure exerted on the exterior of the same disk, only differs from each other by about one two-thousandth part of the latter.”—Annales de Chimie, xxxv. 34.34See the last volume of this Journal, p. 473.2.Considerations relative to Capillary Action, byM. Poisson.—M. Dutrochet, whilst explaining his views relative to the cause of vital movement in plants and animals, stated that if an animal or vegetable membrane were formed into a bag, having a tube of[p195]glass attached to its aperture, and were then filled with a liquid substance, having a strong affinity for another liquid, into which the bag was to be immersed, it would not only have the power of absorbing the latter liquid into its pores, but also, in certain cases, of forcing it up to the top, and even out of the glass tube held in a vertical position. On this point, a difference of opinion with regard to the force of capillarity took place: M. Ampère maintaining that capillary action would raise the fluid to the top of the tube, but not cause its expulsion; while M. Poisson maintained that, in certain cases, the latter effect could be produced. The latter has since then published a note, which we transcribe in part, from theAnnales de Chimie, xxxv. 98.Suppose that two different fluids, A, B, are contained in a vessel, and separated the one from the other by a vertical division; the heights being in an inverse ratio to the densities, so that the points,aandb, in the two faces of the division, and situated in the same horizontal plane, shall support equal and opposite pressures: suppose also that the division is pierced with one or more holes of small diameter, or, in other words, that it is traversed by several very narrow canals, asa,b, perpendicular to the two faces, and which may be regarded at first as filled with air, or any other fluid.If the substance of the division exerts upon each of the two liquids an action superior to the half of that which the liquid has upon itself, each liquid will enter into the canala,b, just as it would rise above its ordinary level in a capillary tube of the same size and substance. It would also be urged, by the excess of pressure which it would exert at the extremity of the canal, against the elasticity of the included air. When the two fluids have penetrated the interior ofa,b, the air will be pushed on both sides in different directions by forces each of which is equal to the primitive pressure augmented by the corresponding capillary force,i. e.augmented by forces proportional, according to the known theory of M. Laplace, to double the action of the tube on the liquid, less the proper action of the liquid itself. It will only be in the case when the capillary force shall be the same on both sides, that the air, after being compressed to a certain degree, will remain at rest: for whenever this force preponderates at one end of the canal, the air will be driven out at the opposite end, and the liquid with the strongest capillary attraction will entirely fill the canal.Suppose this liquid to be A, then let us consider the forces which will act on the portiona,b, of this liquid. At the extremitya, it will be submitted to the attraction of the exterior fluid A: at the extremityb, it will be attracted in the opposite direction by the liquid B. Now the two liquids being different, their attractions will be unequal, and we will suppose that that of B, on the matter[p196]of A, is greater than that of A for itself. As to the action of the canal on the portiona,b, that will be equal, and exerted in contrary directions at its two extremities; it will not, therefore, be either adverse or favourable to the movement of the fluid in the canal: and the same will be the case with respect to the pressures exerted ataandb, by the external liquids, as long as they are equal: nevertheless, the action of the canal, and the external pressures, will prevent the thread of fluid from being broken, so that it will move without interruption in the direction in which it is drawn by the greatest attraction, or fromatob. Hence will result an elevation of the level of B, and, consequently, an increase of pressure at the extremityb, of the passage, and this elevation will proceed until the difference of pressure inaandbshall be equal to that of the attractions exerted by the two fluids A and B, on the threada b; this effect will be produced the more rapidly as the division is pierced with a greater number of passages similar to that which has been considered.Now let us examine what would occur if the division were formed of two others different in their nature, and exactly superposed; exerting no action on one of the liquids, B for example, and one only acting on the other liquid. The liquid B will then retain its original position undisturbed; in consequence of the action it exerts upon itself it cannot penetrate the canala b, just as mercury cannot escape by a capillary aperture made in a barometer-tube. It will be the same with A, when that face of the division which exerts no action upon the liquid is turned towards it; so that how numerous soever the apertures, the two liquids would, under such circumstances, remain separate and preserve their original level. But if the division be turned so that the face which acts upon A shall be in contact with that liquid, it will penetrate the canala bby means of capillary attraction; and the velocity which the liquid urged by this force may acquire, may make it pass that point in the canal where the division changes its nature, and even make it reach the extremity in the liquid B, so that it is possible that the liquid A should entirely fill the canala b, as in the case which has already been examined. Then if we always suppose the attraction of B for A to be superior to that which A has for itself, the threada bwill flow into B until the level of the latter is so far altered that the excess of pressure atbcan balance the difference of attractions exerted by the two liquids ataandb.M. Poisson then observes that, without pretending to assign a cause, exclusive of all others, for the phenomena of absorption by vegetable and animal membranes observed by M. Dutrochet, his object is to show that effects which have at least a great resemblance to these important phenomena, may be produced by capillary action conjoined with the difference of affinity existing between heterogeneous substances without the assistance of electricity, either moving or quiescent. It appears that M. Dutrochet afterwards[p197]found mineral substances, as a piece of slate, might be substituted for the organized tissues; this being the case, the opinion which refers such effects to a general cause, as capillary attraction, acquires more probability.3.Novel Use of the Plough.—Mr. Bruckmann states that he has long thought the plough might be used in levelling roads and clearing the foundations for fortifications. In 1824 he had an opportunity of applying it in the construction of a canal required to furnish a motive force for the service of the rock-salt works of Friedrichshall. The bed was to have a section of 700 square feet, and it had been calculated that the excavations would require 200 men for two years, whereas the king of Wurtemburg wished it to be done in one year from the spring of 1824.Three ploughs were employed; the first had two handles, a coulter, and a share, the latter being in the form of a wedge. This plough was preferred in the beds and gravelly grounds; and it was found advantageous to give it an oscillatory movement by the handles during its progress. Drawn by eight horses, it could turn up 25,000 cubic feet of an argillaceous soil, in three hours; with ten horses it turned up 19,800 cubic feet of a gravelly soil, in the same time. This plough was tried in 1815, against fifteen others of the ordinary kind, in the construction of a watercourse for a mill; all the fifteen were quickly broken by the work.The second plough had two handles and a coulter, but the share had only one cutting edge, which was rounded and with an ear. It was made five times as strong as an ordinary plough, and succeeded well in compact and argillaceous soils, where, with eight horses and four men, it moved 48,000 cubic feet of earth in three hours. In case of fracture ten minutes sufficed to change the coulter and share, and, during the work, 2,300,000 cubic feet of earth were loosened by it.The third plough was smaller and lighter, it had two handles, a coulter, an ear, and a share, the latter lance-shaped. It was used for excavating the sides of the canal, on which the horses attached to the first plough found it difficult to walk because of the inclination. It was worked by ten or twelve men.To establish an accurate comparison between the work of these ploughs and that done by the pickaxe and spade, a piece of ground was wrought solely in the latter manner by six strong working men. The result of a long trial was the breaking of 150 cubic feet of ground by each man in nine hours. Comparing this result with the work of the ploughs, the following are the results:—The first plough did the work of 477 men, the second of 960 men, and the third that of 50 or 60 men. The canal was finished on April 30th, 1825, the ploughs having saved 32,000 days, according to the work-day of a labourer.—Bull. Univ.D. vii. 343.[p198]4.Discovery of Rocks under the Surface of the Sea.—The fishers of the Mediterranean use an apparatus for the discovery of rocks beneath the surface in those places where they wish to cast their nets, which supplies, in a great measure, the insufficiencies of the ordinary means of taking soundings. The method consists in carrying a long and thin cord over the bottom to be examined, and which, when it meets with an obstacle, is stopped by it and becomes folded in the place where it occurs. It will easily be understood, that when a cord has been carried over a certain space without meeting with any resistance, that proof is obtained of the non-existence of rocks or other obstacles, at a depth less than that to which the cord has been sunk; and as the examination can easily be carried on to 100 feet below the surface, it may be said that, wherever such an apparatus has passed unimpeded, the navigation is free. If, on the contrary, some isolated rocks are found during the examination, the place where the cord becomes doubled points out the locality, which may then be determined more accurately by other trials, and the summit and neighbourhood of the submersed rocks be accurately examined by means of soundings.—Annales Marit.;Bull. Univ.F. viii. 44.5.Paper to resist Humidity.—This process, which is due to M. Engle, consists in plunging unsized paper once or twice into clear solution of mastic in oil of turpentine, and drying it by a gentle heat. The paper, without becoming transparent, has all the properties of writing-paper, and may be used for the same purposes. It is especially recommended for passports, workmen’s books, legal papers, &c. When preserved for years it is free from injury, either by humidity, mice, or insects. It is further added, that a solution of caoutchouc will produce even a still better effect.—Kunst und Gewerbe-blatte.6.Professor Amici’s Microscopes.—This distinguished personage has lately exhibited to thesavansof this country two microscopes of his own workmanship,—an achromatic refractor, and a reflector of his own particular invention. The object-glass of his refractor is of a very complicated construction, and is composed of three double-object glasses combined together in the space of about an inch. The flint-glass from which his concaves are formed is of the manufacture of Frauenhofer; his convexes are of Dutch plate, crown-glass, and French plate, separately. Each object-glass detached has but a small aperture, and is of long focus; but when the three are combined together, the angle of aperture is very considerable, and the focus short. By this ingenious arrangement the trouble and difficulty of manipulating deep single-object-glasses of large aperture is avoided; but advantages gained one way, in practical optics, are generally lost in another, and the twelve surfaces of the objective produce a kind of softness and muddiness in[p199]the image strongly contrasted by the effect of a good single triple-glass of equivalent power. When, however, only two of the object-glasses are combined, the effect is very fine. Between the object-glass and eye-glasses is placed one of those prisms originally invented by Sir I. Newton to act as an eye-piece of his telescope, and of which a description may be seen in his correspondence at the end of Dr. Gregory’s Optics. The utility of the introduction of this device appears very questionable in an instrument already so complicated. The diversion of the rays into a course at a right angle to their original progress (merely to give an horizontal instead of a vertical position to the body) is surely no warrant for the employment of two extra refracting surfaces and one reflexion, which cannot fail to have a pernicious influence on the formation of the image. An horizontal position of the body is attained with the utmost facility by a proper construction of the mounting, &c. Setting aside the dulness of the image produced by the numerous refractions, the performance of the instrument on test-objects was highly respectable and satisfactory.The reflector is a modification of the original construction recommended by the Professor, who seems to have profited by the schooling he received from Dr. Goring, and now sails much closer to the wind than he did. His objective metal is now two inches focus, with an aperture of112inch; but half an inch is cut off for the purpose of preventing the bad effect of the marginal rays, so that only 1 inch of the central portion of the metal is employed;—the diameter of the diagonal mirror is also reduced to its proper standard, by which means the blot in the centre of the visual pencil is rendered as small as possible. It may be asserted of this instrument, that it does as much as can possibly be expected from an objective part of 2 inches focus, showing many test-objects faintly, and with much effort; but it is totally unable to compete with deeper ones equally perfect and of the same angular opening. The Professor has, in some of his instruments, reduced the focus of the elliptic metal to112inch, and will, no doubt, gradually slide into the adoption of that radical reform in his instrument, so happily carried into effect in this country by Dr. Goring, in conjunction with Mr. Cuthbert,—at least if the figuration of elliptic metals of310inch focus with210inch of aperture shall not surpass his powers of execution. During the Professor’s stay in this country there was a grand field-day at his hotel, at whichboth his microscopes were tried against the Goringian modification of the reflector, the superior weight of metal of which completely beat every thing opposed to it. For the honour of the Professor it must be stated, that he admitted this defeat with great candour and good sense, and even had some difficulty in believing in the identity of some of the objects used, so differently was the ordinary apparent structure developed by the English improvements on his instrument. It may with safety be averred that no refractor, at least, will ever be[p200]made to surpassDr. Goring’s improved Amician Engiscope; and it seems equally certain that no other reflector will ever be invented capable of the same facilities of application to the examination of both opaque and transparent objects. If Professor Amici has been beaten, it has been done with his own weapons,—the copy has surpassed the original,—the child, by virtue of foreign nursing and tuition, has exceeded the stature and strength of the father.
1.On the combined Action of a Current of Air and the Pressure of the Atmosphere.—The phenomena observed by M. Clement Désormes34, when a flat plate is opposed to air or vapour passing into the atmosphere from an aperture in a plane surface, have been rendered so easy of production by M. Hachette, as to be at the command of any person in any situation. M. Hachette has also accompanied the description of his instruments with elucidations, experiments, and philosophical reasonings.
The first simplification by M. Hachette was to make the nozzle of a pair of double chamber-bellows terminate in the middle of a flat plate; he found that when the bellows were worked, effects were produced opposite the jet of air of the kind described by M. Clement, disks of card and other substances being drawn towards the aperture against the direction of the current. At the same time that he described this experiment, he also announced his having produced the same effects by using a stream of water instead of a stream of air.
Fig.1.Fig.2.
Fig.1.Fig.2.
Fig.1.Fig.2.
Fig.1.
Fig.2.
The apparatus was still further simplified, so as to make the stream of air from the mouth sufficient to produce the effect. A tin tube, A,Fig.1, was soldered to the middle of a round tin plate, in the centre of which was a small orifice, E; three or four small projections of the tin,f f, were left at the edges of the plate, to prevent the disks of paper, card, or metal, from slipping off sideways. The figure is on a scale of one-half. Instead of the tin plate, a piece[p194]of smooth cork may be used, and for the tin tube, a glass tube, or one made by rolling up a piece of paper.
If the tube be held horizontally, or inclining a little upward, and a disk of card or paper be placed loosely against the aperture in the plate, it will be found that, on applying the mouth to the end of the tube, and blowing air through, that the disk will not be driven away, but actually made to apply closely to the surface of the plate; and if turned towards the ground it will be found to remain opposite the hole, and not to fall until the current of air is stopped. Even a plate of tin may in this way be suspended by a current of air; which at first would be supposed to conjoin with gravity in forcing it to the ground. When the disk is flexible and slightly elastic, a heavy sound, and sometimes even a shrill tone, is produced by the vibrations of the plate.
In explanation of this experiment, M. Hachette says, “The air is pushed from the mouth A of the tube, towards the orifice E of the plate; it strikes the part of the disk opposed to this orifice, and the mean pressure on that part is greater than the pressure of the atmosphere. The blown air then takes place of that between the plate and the disk opposed to it; it moves in this interval with a velocity decreasing from the edges of the aperture: the elastic force of this air decreases at the same time, so that its mean pressure between the plate and the inner face of the disk becomes less than the atmospheric pressure; and as this last pressure is exerted on the whole external face of the disk H, I, this disk, subject at the same time to the two contrary pressures on its opposing faces, obeys the greater, and is pushed towards the plate C D.”
“It is not necessary that the disk, C D, should be near the orifice E, of the tube A E. LetFig.2 be an instrument composed of a hollow cylinder, C D F G, and a flat border of the dimensions C″ F, or G D″. Let a tube, A E, be fixed to the bottom of the cylinder, the orifice E having a diameter of about three millimeters (0.12 of inch). If air be blown in at A, against the disk, H I, in the neighbourhood of the flat border, the disk will be urged towards the orifice E. This instrument is also delineated on a scale of one half. The disk, with the attached weight, weighs about 12 grammes (184.87 grains), being 54 millimeters in diameter; the pressure of the atmosphere upon it equals 23 kilogrammes: from which it follows that, in this experiment, the pressure of the air blown upon the inner surface of the disk, and the atmospheric pressure exerted on the exterior of the same disk, only differs from each other by about one two-thousandth part of the latter.”—Annales de Chimie, xxxv. 34.
34See the last volume of this Journal, p. 473.
34See the last volume of this Journal, p. 473.
2.Considerations relative to Capillary Action, byM. Poisson.—M. Dutrochet, whilst explaining his views relative to the cause of vital movement in plants and animals, stated that if an animal or vegetable membrane were formed into a bag, having a tube of[p195]glass attached to its aperture, and were then filled with a liquid substance, having a strong affinity for another liquid, into which the bag was to be immersed, it would not only have the power of absorbing the latter liquid into its pores, but also, in certain cases, of forcing it up to the top, and even out of the glass tube held in a vertical position. On this point, a difference of opinion with regard to the force of capillarity took place: M. Ampère maintaining that capillary action would raise the fluid to the top of the tube, but not cause its expulsion; while M. Poisson maintained that, in certain cases, the latter effect could be produced. The latter has since then published a note, which we transcribe in part, from theAnnales de Chimie, xxxv. 98.
Suppose that two different fluids, A, B, are contained in a vessel, and separated the one from the other by a vertical division; the heights being in an inverse ratio to the densities, so that the points,aandb, in the two faces of the division, and situated in the same horizontal plane, shall support equal and opposite pressures: suppose also that the division is pierced with one or more holes of small diameter, or, in other words, that it is traversed by several very narrow canals, asa,b, perpendicular to the two faces, and which may be regarded at first as filled with air, or any other fluid.
If the substance of the division exerts upon each of the two liquids an action superior to the half of that which the liquid has upon itself, each liquid will enter into the canala,b, just as it would rise above its ordinary level in a capillary tube of the same size and substance. It would also be urged, by the excess of pressure which it would exert at the extremity of the canal, against the elasticity of the included air. When the two fluids have penetrated the interior ofa,b, the air will be pushed on both sides in different directions by forces each of which is equal to the primitive pressure augmented by the corresponding capillary force,i. e.augmented by forces proportional, according to the known theory of M. Laplace, to double the action of the tube on the liquid, less the proper action of the liquid itself. It will only be in the case when the capillary force shall be the same on both sides, that the air, after being compressed to a certain degree, will remain at rest: for whenever this force preponderates at one end of the canal, the air will be driven out at the opposite end, and the liquid with the strongest capillary attraction will entirely fill the canal.
Suppose this liquid to be A, then let us consider the forces which will act on the portiona,b, of this liquid. At the extremitya, it will be submitted to the attraction of the exterior fluid A: at the extremityb, it will be attracted in the opposite direction by the liquid B. Now the two liquids being different, their attractions will be unequal, and we will suppose that that of B, on the matter[p196]of A, is greater than that of A for itself. As to the action of the canal on the portiona,b, that will be equal, and exerted in contrary directions at its two extremities; it will not, therefore, be either adverse or favourable to the movement of the fluid in the canal: and the same will be the case with respect to the pressures exerted ataandb, by the external liquids, as long as they are equal: nevertheless, the action of the canal, and the external pressures, will prevent the thread of fluid from being broken, so that it will move without interruption in the direction in which it is drawn by the greatest attraction, or fromatob. Hence will result an elevation of the level of B, and, consequently, an increase of pressure at the extremityb, of the passage, and this elevation will proceed until the difference of pressure inaandbshall be equal to that of the attractions exerted by the two fluids A and B, on the threada b; this effect will be produced the more rapidly as the division is pierced with a greater number of passages similar to that which has been considered.
Now let us examine what would occur if the division were formed of two others different in their nature, and exactly superposed; exerting no action on one of the liquids, B for example, and one only acting on the other liquid. The liquid B will then retain its original position undisturbed; in consequence of the action it exerts upon itself it cannot penetrate the canala b, just as mercury cannot escape by a capillary aperture made in a barometer-tube. It will be the same with A, when that face of the division which exerts no action upon the liquid is turned towards it; so that how numerous soever the apertures, the two liquids would, under such circumstances, remain separate and preserve their original level. But if the division be turned so that the face which acts upon A shall be in contact with that liquid, it will penetrate the canala bby means of capillary attraction; and the velocity which the liquid urged by this force may acquire, may make it pass that point in the canal where the division changes its nature, and even make it reach the extremity in the liquid B, so that it is possible that the liquid A should entirely fill the canala b, as in the case which has already been examined. Then if we always suppose the attraction of B for A to be superior to that which A has for itself, the threada bwill flow into B until the level of the latter is so far altered that the excess of pressure atbcan balance the difference of attractions exerted by the two liquids ataandb.
M. Poisson then observes that, without pretending to assign a cause, exclusive of all others, for the phenomena of absorption by vegetable and animal membranes observed by M. Dutrochet, his object is to show that effects which have at least a great resemblance to these important phenomena, may be produced by capillary action conjoined with the difference of affinity existing between heterogeneous substances without the assistance of electricity, either moving or quiescent. It appears that M. Dutrochet afterwards[p197]found mineral substances, as a piece of slate, might be substituted for the organized tissues; this being the case, the opinion which refers such effects to a general cause, as capillary attraction, acquires more probability.
3.Novel Use of the Plough.—Mr. Bruckmann states that he has long thought the plough might be used in levelling roads and clearing the foundations for fortifications. In 1824 he had an opportunity of applying it in the construction of a canal required to furnish a motive force for the service of the rock-salt works of Friedrichshall. The bed was to have a section of 700 square feet, and it had been calculated that the excavations would require 200 men for two years, whereas the king of Wurtemburg wished it to be done in one year from the spring of 1824.
Three ploughs were employed; the first had two handles, a coulter, and a share, the latter being in the form of a wedge. This plough was preferred in the beds and gravelly grounds; and it was found advantageous to give it an oscillatory movement by the handles during its progress. Drawn by eight horses, it could turn up 25,000 cubic feet of an argillaceous soil, in three hours; with ten horses it turned up 19,800 cubic feet of a gravelly soil, in the same time. This plough was tried in 1815, against fifteen others of the ordinary kind, in the construction of a watercourse for a mill; all the fifteen were quickly broken by the work.
The second plough had two handles and a coulter, but the share had only one cutting edge, which was rounded and with an ear. It was made five times as strong as an ordinary plough, and succeeded well in compact and argillaceous soils, where, with eight horses and four men, it moved 48,000 cubic feet of earth in three hours. In case of fracture ten minutes sufficed to change the coulter and share, and, during the work, 2,300,000 cubic feet of earth were loosened by it.
The third plough was smaller and lighter, it had two handles, a coulter, an ear, and a share, the latter lance-shaped. It was used for excavating the sides of the canal, on which the horses attached to the first plough found it difficult to walk because of the inclination. It was worked by ten or twelve men.
To establish an accurate comparison between the work of these ploughs and that done by the pickaxe and spade, a piece of ground was wrought solely in the latter manner by six strong working men. The result of a long trial was the breaking of 150 cubic feet of ground by each man in nine hours. Comparing this result with the work of the ploughs, the following are the results:—The first plough did the work of 477 men, the second of 960 men, and the third that of 50 or 60 men. The canal was finished on April 30th, 1825, the ploughs having saved 32,000 days, according to the work-day of a labourer.—Bull. Univ.D. vii. 343.[p198]
4.Discovery of Rocks under the Surface of the Sea.—The fishers of the Mediterranean use an apparatus for the discovery of rocks beneath the surface in those places where they wish to cast their nets, which supplies, in a great measure, the insufficiencies of the ordinary means of taking soundings. The method consists in carrying a long and thin cord over the bottom to be examined, and which, when it meets with an obstacle, is stopped by it and becomes folded in the place where it occurs. It will easily be understood, that when a cord has been carried over a certain space without meeting with any resistance, that proof is obtained of the non-existence of rocks or other obstacles, at a depth less than that to which the cord has been sunk; and as the examination can easily be carried on to 100 feet below the surface, it may be said that, wherever such an apparatus has passed unimpeded, the navigation is free. If, on the contrary, some isolated rocks are found during the examination, the place where the cord becomes doubled points out the locality, which may then be determined more accurately by other trials, and the summit and neighbourhood of the submersed rocks be accurately examined by means of soundings.—Annales Marit.;Bull. Univ.F. viii. 44.
5.Paper to resist Humidity.—This process, which is due to M. Engle, consists in plunging unsized paper once or twice into clear solution of mastic in oil of turpentine, and drying it by a gentle heat. The paper, without becoming transparent, has all the properties of writing-paper, and may be used for the same purposes. It is especially recommended for passports, workmen’s books, legal papers, &c. When preserved for years it is free from injury, either by humidity, mice, or insects. It is further added, that a solution of caoutchouc will produce even a still better effect.—Kunst und Gewerbe-blatte.
6.Professor Amici’s Microscopes.—This distinguished personage has lately exhibited to thesavansof this country two microscopes of his own workmanship,—an achromatic refractor, and a reflector of his own particular invention. The object-glass of his refractor is of a very complicated construction, and is composed of three double-object glasses combined together in the space of about an inch. The flint-glass from which his concaves are formed is of the manufacture of Frauenhofer; his convexes are of Dutch plate, crown-glass, and French plate, separately. Each object-glass detached has but a small aperture, and is of long focus; but when the three are combined together, the angle of aperture is very considerable, and the focus short. By this ingenious arrangement the trouble and difficulty of manipulating deep single-object-glasses of large aperture is avoided; but advantages gained one way, in practical optics, are generally lost in another, and the twelve surfaces of the objective produce a kind of softness and muddiness in[p199]the image strongly contrasted by the effect of a good single triple-glass of equivalent power. When, however, only two of the object-glasses are combined, the effect is very fine. Between the object-glass and eye-glasses is placed one of those prisms originally invented by Sir I. Newton to act as an eye-piece of his telescope, and of which a description may be seen in his correspondence at the end of Dr. Gregory’s Optics. The utility of the introduction of this device appears very questionable in an instrument already so complicated. The diversion of the rays into a course at a right angle to their original progress (merely to give an horizontal instead of a vertical position to the body) is surely no warrant for the employment of two extra refracting surfaces and one reflexion, which cannot fail to have a pernicious influence on the formation of the image. An horizontal position of the body is attained with the utmost facility by a proper construction of the mounting, &c. Setting aside the dulness of the image produced by the numerous refractions, the performance of the instrument on test-objects was highly respectable and satisfactory.
The reflector is a modification of the original construction recommended by the Professor, who seems to have profited by the schooling he received from Dr. Goring, and now sails much closer to the wind than he did. His objective metal is now two inches focus, with an aperture of112inch; but half an inch is cut off for the purpose of preventing the bad effect of the marginal rays, so that only 1 inch of the central portion of the metal is employed;—the diameter of the diagonal mirror is also reduced to its proper standard, by which means the blot in the centre of the visual pencil is rendered as small as possible. It may be asserted of this instrument, that it does as much as can possibly be expected from an objective part of 2 inches focus, showing many test-objects faintly, and with much effort; but it is totally unable to compete with deeper ones equally perfect and of the same angular opening. The Professor has, in some of his instruments, reduced the focus of the elliptic metal to112inch, and will, no doubt, gradually slide into the adoption of that radical reform in his instrument, so happily carried into effect in this country by Dr. Goring, in conjunction with Mr. Cuthbert,—at least if the figuration of elliptic metals of310inch focus with210inch of aperture shall not surpass his powers of execution. During the Professor’s stay in this country there was a grand field-day at his hotel, at whichboth his microscopes were tried against the Goringian modification of the reflector, the superior weight of metal of which completely beat every thing opposed to it. For the honour of the Professor it must be stated, that he admitted this defeat with great candour and good sense, and even had some difficulty in believing in the identity of some of the objects used, so differently was the ordinary apparent structure developed by the English improvements on his instrument. It may with safety be averred that no refractor, at least, will ever be[p200]made to surpassDr. Goring’s improved Amician Engiscope; and it seems equally certain that no other reflector will ever be invented capable of the same facilities of application to the examination of both opaque and transparent objects. If Professor Amici has been beaten, it has been done with his own weapons,—the copy has surpassed the original,—the child, by virtue of foreign nursing and tuition, has exceeded the stature and strength of the father.