process of charging, the electric fluid is forced into it along with the wire in the inside of the coating, where it instantly and equally spreads itself over the whole coated part, and at the same time, though with difficulty, and consequently gradually, it spreads itself over the uncoated part, taking the condensed film of humidity for its conductor, as it proceeds from the edges of the coating upwards towards the mouth of the jar, according to the arrangement of the particles of moisture, and rises higher or lower, depending entirely on their arrangement, and the force with which it is repelled from the machine. If the conducting particles be almost uniformly diffused over the uncoated part, the whole jar, in the inside, will become charged, though the uncoated part will be charged in a much less degree than the coated, on account of the imperfection of the conducting particles which has adhered to its surface; no coruscations will be perceived on account of the gradual and equal diffusion of the electric fluid over its inside surface: and though the charging be continued, yet, if the exhaled conducting particles be favourably diffused, no spontaneous explosion will happen from one coating to the other, along the uncoated surface, but the jar will either be perforated, or, if it be of sufficient strength to resist that effect, the electric fluid will be seen to run in a stream over the mouth of the jar, as quickly as the machine supplies it. Whenever a spontaneous electric explosion happens, it must be from a body of sufficient bulk and conducting property to contain that quantity of electric fluid at that point from which it explodes, otherwise no explosion ever happens. But the humid conducting particles are just sufficient merely to admit the electric fluid, by the action of the machine, to be spread over the surface of the glass, but in no part of sufficient density either to receive or contain an explosion. If, therefore, a spontaneous explosion do happen, it must either proceed from the inside coating, or the wire which is connected with it to the outside; and, if we examine the state of the coating, we shall understand, that the edge of the coating (from which part only it is ever possible to explode), and also above it, to a short distance upwards, is as strongly charged as the coated part; and by the action of the machine it is so strongly loaded with electric fluid, that it is repulsive in all directions, which keeps back, or entirely stops, a spontaneous explosion from the edge of the coating. With regard to the wire, the only place from which it explodes spontaneously, is that part which is nearly of an equal height with the edge of the mouth of the jar. The fluid is nearly as much condensed on this part as on the other, so that an explosion from the wire is hindered by the same cause as from the coating. A jar, under such circumstances cannot, therefore, explode spontaneously; but the fluid will run over the edge of the jar as quickly as the machine furnishes it, when its charging capacity is full.

I have stated, at page 530, that a jar of the dimensions there given, being clean and dry, can only contain a charge sufficient to

fuse two inches of a certain wire, and when breathed into, its charging capacity will be so much increased, that it will contain a charge sufficient to fuse eight inches of the same sort of wire; and a battery of fifteen jars, in the first-mentioned state, can only fuse twenty inches, and in the last-mentioned, sixty inches. This increased charging capacity proceeds, no doubt, from the particles of moisture, though not from their acting as a coating, as has been supposed, but by their being brought into a state or capacity of resisting a spontaneous explosion, so that a stronger charge is forced in upon the coated part. Some of the electric fluid which was forced upon the uncoated part to a certain height (perhaps half an inch, more or less, according to the degree of dampness, and the saturation of the particles) may, indeed, be discharged along with that from the coated part; but this is of little importance, and by no means capable of producing that increased effect, which, as I have shewn by experiment, would require an addition of seven jars to a battery of fifteen.

Electro-Magnetic Locomotive Carriage.*

A TRIAL of this very ingenious machine, constructed by Mr. Davidson, was made on Thursday week, on the Edinburgh and Glasgow Railway, in presence of a number of gentlemen, many of whom were eminent for their scientific knowledge. The construction of the carriage is the first attempt which has been made in this country to apply the powers of electro-magnetism to railway traffic, and from the success which attended this trial sanguine hopes may be entertained that the period is not distant when it will either supersede, in many cases, the employment of steam, or lend a powerful aid to this mighty instrument in all the operations in which it is at present employed. The carriage was impelled along the railway about a mile and a half, travelling at the rate of four miles an hour, a rate which might be increased by giving greater power to the batteries, and enlarging the diameter of the wheels. We understand that the carriage was built at the expense of the Railway Company, and we cannot but congratulate them in having the discernment to employ Mr. Davidson, a gentleman of much practical knowledge and talent, to whose genius great discoveries have been made in electro-magnetism, by whom the carriage was projected, and to whose unwearied exertions the practicability of the scheme is almost placed beyond a doubt.

The dimensions of the carriage is sixteen feet long by seven feet wide, and is propelled by eight powerful electro-magnets. The carriage is supported by four wheels of three feet in diameter. On each of the two axles there is a wooden cylinder, on which are fastened three bars of iron at equal distances from each other, and extending

Edinburgh Evening Courant.

from end to end of the cylinder. On each side of the cylinder, and resting on the carriage, there are two powerful electro-magnets. When the first bar on the cylinder has passed the faces of two of these magnets, the current of galvanism is then let on to the other two magnets they immediately pull the second bar until it comeş opposite them. The current is then cut off from these two magnets, and is let on to the other two. Again they pull the third bar until it comes opposite, and so on-the current of galvanism being always cut off from the one pair of magnets when it is let on to the other.

The manner in which the current is cut off and let on is simply thus-At each end of the axles there is a small wooden cylinder, one-half of which is covered by a hoop of copper; the other is divided alternately with copper and wood (three parts of wood and three of copper). One end of the coil of wire which surrounds the four electro-magnets, presses on one of the cylinders, on the part which is divided with copper and wood; the other end of the coil presses on the other cylinder in the same manner. One end of the wires or conductors which comes from the battery, presses constantly on the undivided part of the copper on each cylinder. When one of the iron bars on the wooden cylinder has passed the faces of two magnets, the current of galvanism is let on to the other two magnets, by one end of the coil which surrounds the magnets, passing from the wood to the copper, and thereby forming a connexion with the battery. This wire continues to press on the copper until the iron bar has come opposite the faces of the two magnets, which were thus charged with galvanism. On its coming into that position, the current is cut off from these two magnets, by the wire or rod of copper passing from the copper to the wood, and thereby breaking the connexion with the battery. But when the wire or rod of copper leaves the copper on the one cylinder, it leaves the wood, and passes to the copper on the other cylinder at the other end of the axle, and in so doing connects the other two magnets with the battery, and they pull the next iron bar in the same manner. At the other end of the carriage there are other four magnets, and wooden cylinder, with iron bars arranged in the same manner.

The battery which is used for propelling the machine is composed of iron and zinc plates immersed in dilute sulphuric acid, the iron plates being fluted so as to expose greater surface in the same space. The weight propelled was about six tons.

Method of detecting the Adulteration of Cane or Beet-root Sugar with Sugar of Fecula. By M. E. KRANTY.*

[To detect the Admixture of these two kinds of Sugar.]

To detect the presence of the sugar of fecula, two grammes of the suspected specimen are to be dissolved in a flask, in thirty grammes of distilled water; the liquor is then to be filtered, and two deci

• Journal de Chimie Médicale, 1842.

grammes of potash in alcohol and one decigramme of sulphate of copper are to be added; the whole to be well stirred about to accomplish complete dissolution. The flask is afterwards to be corked, and the subsequent appearances observed.

Should the sugar under examination contain sugar of fecula, a red precipitate will be observed some time after mixing; and if we operate on a large quantity, the transformation of the cupreous salt into a protoxide will be completely accomplished in twenty-four hours. The solution loses all its blue or green colour, and not a trace of copper is to be found in it.

If we operate on pure sugar from the cane, or from beet-root, no red precipitate is formed from the same process, even after eight days' standing. If the mixture contain equal parts of the pure and impure sugars, the precipitation will be completed in about twenty hours. If the impure be only 2.5 per cent., a slight red precipitate is observed in twenty-four hours; but the solution will not become colourless in less than eight or ten days.

Thunder Storm at Bristol.

DURING the severe thunder storm on Thursday fortnight, a serious accident occurred at the Great Western Cotton Works, St. Philip's, Bristol. At about twenty minutes before five o'clock in the afternoon, the electric fluid struck the meter-house, and completely destroyed the large gas meter, the erection of which had just cost the company £130. The iron face of the meter was split in pieces, and the gas which was in the cylinder (fortunately it was turned off at the main) being ignited by the electric fluid, exploded, and large pieces of iron, one of them weighing about 100lbs., were thrown with such violence against a wall twenty-five feet distant as to produce considerable indentations in portions of the masonry. The meter

house is erected in front of the weaving room, in which between 500 and 600 girls were at work at the time. The main gas pipe, which is attached to the meter, passes through the wall and descends beneath the floor of this room, and as a large portion of it was blown off, it seems almost a miracle that no lives were lost. Several of the girls fell fainting on the floor, others rushed to the door to escape from the factory, and all was confusion and alarm, but no one was hurt.

THE ANNALS

OF

ELECTRICITY, MAGNETISM,

AND

CHEMISTRY;

AND

GUARDIAN OF EXPERIMENTAL SCIENCE.

NOVEMBER, 1842.

On Gravitation.

SUPPOSE that an elastic compressing fluid pervaded the universe, such as electricity, or some modification of it, the following communication is an attempt to demonstrate that were a soft inelastic body, semi-fluid, introduced into it, that the inelastic body would be equally pressed on all sides, and would take the form of a globe; and secondly, that were two or more bodies, as A and B, placed in that elastic atmosphere, such as the earth and sun, that the pressure of the elastic atmosphere on each body would not be equal in every direction as on the single body; that the pressure in a

direct line between the bodies A and B,

Α

A

C

B

tending to keep them asunder from each other, or from the centre c, would not be equal to the pressure in the opposite direction, forcing them towards that centre.

This is the conclusion arrived at, which is in opposition to the generally received opinion, that action and reaction in all cases is equal and contrary in fluids as well as in solids. It is generally conceived that the fluid exerts the same force to press A and B asunder as it does in pressing them together, which I have attempted to show is not the fact; and my object in this communication is to give the reasons I have for this opinion to the public, so that they may be corrected if wrong, and the fallacy of the reasoning pointed out, or its truth confirmed.

That a single soft inelastic body, if it existed alone in an elastic compressing atmosphere, would be forced into the form of a globe by the elastic fluid pressing it equally on all sides, is a proposition that will not be disputed: but that if two bodies were introduced into that atmosphere, then the pressure on them would not be equal Ann. of Elec. Vol. IX, No. 53, Nov., 1842.

Y