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tow I place some loose gunpowder. Now, by this arrangement, the electric fluid will have to traverse the whole of these bodies; first, through the paper and tinfoil; next through the tow and turpentine; then through the tow and rosin, and after leaving that combination of inflammables, it will traverse the loose gunpowder, and proceed to the outside of the jar. The results of the discharge of the large jar, from a high intensity, are easily predicted by those conversant in experiments of this kind; but to others there may appear to be something mysterious in them, Now we will discharge the jar. The result on the two balls of tow are probably such as you might be led to expect-both are set on fire; but what has become of the gunpowder? It also is an inflammable body, but it is not ignited, nor, indeed, is it left in its place. It is blown away, and scattered in every direction, from the axis of the electric path; not even a single grain is left where the fluid passed through the heap.

You will probably ask how I know the path of the discharge through the gunpowder, now that it is gone from the place? This is very easily ascertained; for if you will examine the card on which the powder was placed, you will find it perforated by the electric fluid, and by calling to your recollection the position of the gunpowder on the card previous to the discharge, you will identify the perforation with the centre of the base of the heap. Consequently the electric fluid, which has so obviously pierced the card, must have traversed the gunpowder from the pointed wire above it, to the perforation of the card.

But you will observe also that this perforation is the centre of the blank space on the card left by the gunpowder. Hence we have, by this fact, a complete demonstration not only of the existence of the lateral force of the discharge, but also a demonstration of that force being exerted on every side alike.

Now call to your recollection that you have already seen that no card can be pierced by a discharge of this jar when a wet string forms a part of the circuit; and that I have shown you that, through such a circuit the velocity is much lessened. From a knowledge of these facts you are led to understand that the velocity, and consequently the mechanical action of this discharge, must have been great, otherwise the card could not have been perforated. Moreover, the scattering of the gunpowder is another manifestation of a great velocity and consequent momentum of the discharged electric fluid.

Now let us examine the paper and tin foil in the other part of the circuit. Both are perforated: another indication of the great electro-momentum attending the discharge of the jar through this compound circuit.

Let us now make a slight change in this experiment, by introducing a piece of wet thread as a portion of the circuit. The jar shall be charged to the same intensity as before, but the result of the discharge will be very different. Neither the paper nor the tin foil will be perforated; neither of the balls of tow will be burnt, but you will see the gunpowder exploded. If, however, I were to enlarge

the lateral dimensions of the aqueous part of the circuit so as to increase the velocity of the fluid, and thus permit it to move in a more compact body, the paper and tin foil would suffer perforation, and the whole of the inflammables would take fire.

It is a remarkable fact that the gunpowder should not ignite under the same circumstances that accomplish the ignition of the other bodies; but time seems to be an essential element to insure success, and it is a matter of no consequence what are the means employed to give sufficient time for the electric fluid to be in contact with the gunpowder, for it will invariably ignite provided a sufficient period of time be procured, and the quantity of electric fluid transmitted be sufficient also.

Gunpowder has been ignited by a series of heavy sparks from a large prime conductor transmitted through a compact cartridge; but, in this case, the quantity of fluid was great, and the velocity lessened by the retarding power of the gunpowder itself, which being confined could not be blown away, Heavy discharges, with great velocities, from a battery of jars, have also been the means of igniting gunpowder; but in those cases the ignition of the powder was a secondary effect, arising from the wire which led the fluid into the cartridge being intensely heated by the discharge of the electric battery. Formerly it was a common practice to mix the gunpowder, intended to be exploded by electricity, with iron filings, which, becoming red hot by the discharge, set fire to the gunpowder as a matter of course. And we are not without those, at the present day, who conceal a thin platinum wire in the powder, for the purpose of accomplishing the explosion.

Another method of illustrating the fact that the ignition of loose gunpowder requires time for the electric fluid to be amongst its particles, and a consequent abatement of the velocity with which it moves through a circuit of good conductors, is that of first placing a portion in a circuit of that kind; transmit through it a discharge of a certain degree of intensity of the jar, and you will find the powder blown away as in the compound circuit of paper, tin foil, tow, and gunpowder, when all the rest of the circuit was metal. Having satisfied yourself on that point, next vary the arrangement, by placing a wet thread in the circuit. The discharge of the jar from the same degree of intensity, explodes the powder.

I have already shown you that, by an introduction of the moistened thread as a part of the circuit, the electro-momentum is sufficiently abated to be deprived of the power of communicating a shock to a person through which the fluid passes. Now, from that fact, and from the fact also of accomplishing the ignition of gunpowder when the electro-momentum is thus abated, there can be no reason why the gunpowder should not be ignited by the same discharge of the jar, in the circuit of which a person is placed without experiencing

the shock.

Now, in order to give a striking illustration of this fact, I will place a battery of six miniature pieces of ordnance in one part of

the circuit, and myself in another part of it. When the jar is charged to the usual high intensity, I will operate in the capacity of discharging-rod, by presenting the brass ball which I hold in my hand towards the ball of the jar. The result is the simultaneous discharge of the six pieces of ordnance, but not the slightest shock is experienced by myself, although the electric fluid that discharged the guns traversed my arms and chest, prior to its arriving at them. Glass tubes, filled with water, have been employed in place of the wet string, in the process of firing gunpowder by electric discharges; but if the tube be too wide, the electro-momentum would be too great for any person to stand in the circuit without experiencing a severe blow; and even by long use of a narrow tube the electric momentum becomes too great for any person to stand in its way. I have employed a glass tube of narrow bore for several successive years, but I found that it gradually augmented the velocity of the transinitted electric fluid, till eventually I could not ignite gunpowder by its use unless, indeed, I considerably augmented the quantity of fluid transmitted. This circumstance, I afterwards found, was owing to the nitric acid that had been formed by previous discharges, from the atmospheric air which the water held in solution, thus increasing its conduction, and giving greater freedom to the electric transmisssion.

This fact, which I have not seen mentioned in any other place, would not happen if a new portion of water were employed in every experiment, and the inside of the tube well cleaned. Another fact that I sometimes meet with, when operating on gunpowder, is that of setting the string on fire, at one or both of its ends, when they happen to get too dry by previous discharges.

Shortly after the discovery of electro-magnetism was made known in England, Sir Humphrey Davy magnetized steel needles by electrical discharges from a battery of Leyden jars; as will be seen by a reference to his excellent paper in these Annals.* But I am not aware that those experiments were ever varied by a change in the character of the circuit, prior to those which I published in 1826, in the Phil. Magazine. By those experiments I showed that, unless the electric fluid has a considerable momentum, steel needles are not magnetized by its influence whilst traversing a circuit from the Leyden jar.†

• Vol. vii. † See the first and second papers in No. 47, of these Annals.

EDITORIAL NOTICES.

are

We have heard nothing further respecting the enquiries of T. H. than that our letter, a copy of which appears at page 221, Vol. 6, had been received. The Editor of the Nautical Magazine, merely acknowledged it on the cover of his No. for April, 1841. The "Reviews" which Mr. B. thinks necessary to be continued, not lost sight of. We have a long time ago been advised, by one of the first chemical philosophers in the land, to carry them on in regular series. Want of time alone, has prevented us undertaking the arduous task. We are aware of the importance of such an undertaking were it for no other purpose than that of exhibiting, to the writer of those papers, the propriety and importance of rectitude, candour, and consistency. We are of opinion that a series of commentaries, properly conducted, and in the same order that the papers have appeared, would be exceedingly interesting.

Dr. Faraday has refused answering Dr. Hare's second letter, Annals, Vol. 7, p. 351, and declined any further public discussion with him on the points at issue.-Silliman's American Journal.

Prize Volumes for the latter half year of 1842.

1st. For the paper descriptive of a more powerful and economical voltaic battery than any, at present, known. The test to be, decomposition of acidulated water, with the terminal metals at one inch asunder.

2nd. For another voltaic battery; conditions as before. Test, the decomposition of pure water, with terminals four inches asunder

3rd. For a thermo-electric battery, superior to any now known, differently constructed, and more economical. Test, the ignition of the greatest length of platinum wire, ofth of an inch diameter. 4th. For any magnet that will suspend 1 cwt., with the cross-piece at one inch distance from the poles.

END OF VOLUME EIGHT.

INDEX TO VOLUME EIGHT.

A.

Page.

Ampére, M...

Adams, Dr. Samuel, his Experiments and Observations on

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Light
Agassiz, Professor, on an undescribed species of Sturgeon

384

210

Airy, Professor, Astronomer Royal, on Magnetic Variation 119

Arago, M., on Electro-Gilding

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337

217

Armstrong, Mr.

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Artesian Wells

498

Apjohn, Dr., on Pyrope

on the Diurnal Fluctuations of the Barometer
on the Voltaic Pile

Arria, M., on the Induction of Electric Currents
Asphyxia, on the Treatment of

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Ballard, Professor M., on Bioxalate of Ammonia
Ball, Mr., on an undescribed species of Sturgeon

Barlow, Professor

Bante, M., on Electro-Gilding

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180

(Note). 47

..

..

Barnard, Professor, F.A.P., on the Daguerreotype Process
Barometer, Diurnal Fluctuations of

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337, 341

217

255

209

Bassett, John, Esq., M.P., on the Machinery for Raising Miners 237
Becquerel, M., his Balance Electrometer

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Edmund, on the Constant Voltaic Battery 454
Bennet, the Rev. Abraham, on Electricity by Evaporation 354
by Simple Contact 422

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Blee, Mr. Robert, Jun., on the Longevity of Miners

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