Imágenes de páginas
PDF
EPUB
[merged small][ocr errors][merged small][merged small][merged small][ocr errors][ocr errors]

WHEN

Arr. I. Experiments and Obfervations made with a view to point out

ihe Errors of the prefent received Theory of Ele&ricity; and which tend in their Progress to establish a new System, on Principles more cona formable to the fimple Operations of Nature. By the Rev. John Lyon, of Dover, Kent. 4to. 12 s. Boards, Dodfley. 1780.

HEN a Writer, who has evidently taken considerable

pains to investigate a particular subject by a great variety of experiments, and who has, in general, expressed their resalts without arrogance, fails in his purpose of informing the world; we feel a fincere pain in discharging our duty to the Public, by pointing out his defects. That duty, however, must be performed by us on the present occafion; not as partisans of Dr. Franklin, but as friends to truth, and well-wishers to the progress of real science.

If the Franklinian system of electricity is to be overturned ; its demolition must be effected by means very different from those employed by the present Author. It undoubtedly has its difficulties but what subject of human investigation is free from them? It may have its errors, as is asserted in the title-page of the present work: but this publication, we may safely affirm, is better fitted to exhibit the errors and oversights of its Author, than those of Dr. Franklin.-But let us hear what the Writer himself fays, in his Introduction.

He there informs us, that, above ten years ago, he had reason to believe, that the present received hypothetical System of electricity could not be founded on truth. An apprehenfion, however, that he might be mistaken, prevented his offering his observations to the public. Returning afterwards to his first pursuit, he found · more convincing proofs to confirm his forVol. LXIV.

B

mer

mer opinion, that the received theory, as established by Dr. Franklin, is erroneous ;-and has since prosecuted this study with an unwearied zeal.'

He was foon fatisfied of the permeability of glafs to the electric fluid. He • drew up his opinion on this subject, grounded upon and confirmed by experiments, and offered it to a learned society :' but as I happened, adds Mr. Lyon, to differ from the popular theory, the persons to whom my paper was ada dreffed, did not deign to submit it to the inspection of the Publie.'-On this occasion, the Author formed the resolution of compiling the present work; which should not only contain his proofs of the erroneousness of the popular theory, but likewife such an account of the principles of ele&tricity, as would be sufficient to initiate a young beginner in the elements of this branch of science,

He accordingly first undertakes to explain the general properties of the electric Auid, according to the present received theory; but does not proceed far in this explanation, before he denies the impermeability of glafs to the electric matter.' Paffing over fome frivolous experiments, brought in proof of his doctrine on this head; we Thall attend to his 6th Experiment, which we shall give in his own words: • Exper. VI. To fhew that a large Jar may be discharged through

a Pane of Glass, without injuring it in the least Degree.' < Take a pane of glass 10 or 12 inches diameter, more or less, according to the lize of your jar, and place it upon a wire under the end of the conductor, where you fix your jar. Let the end of the wire be hooked to a sharp pin, placed perpendicularly to the horizon, with the point close to the under-surface of the pane, and opposite to another sharp point upon the upper furface of the glass, upon which also the vial or jar is to be placed ; so as to be in contact with the last-mentioned point. Fix one end of a large conducting bow, with a glass handle, to the other end of the wire lying under the glass; and when the jar is charged, if you suddenly touch the knob of the jar with the other end of the conducting bow, the jar will be discharged with a spark, andi a snap.'

This experiment is described rather obscurely; but the mean, ing of it we apprehend to be this :-that a charged jar may be discharged, though the circuit be interrupted by a pane of glass interposed: the electric matter, that issues from the infide of the jar, palling from the point of one pin, through the substance of the pane, and without cracking or perforating it, to the point of another pin placed directly opposite to it, and which is connected with the outside of the jar.

Were there no error in the relation of this experiment, it would afford a most decisive proof against the supposed im?

permeability

permeability of glass, at leaft with respect to an electric charges and would, in fact, thake the Franklinian system to its very Foundation. Though we might content ourselves with giving this experiment, as here 'related, a flat contradiction; we can not help expressing our surprise, that the Author Thould not dwell more particularly on a refult fo very decifive against the Franklinian doctrine; though he could not but be consciousy that the generality of electricians consider a pane of glass as an impenetrable barrier to the courfe of an electrical discharge. He must be fenfible, that they would be anxious to know, whes ther the experiment fucceeds invariably, or how often, and what are the circumftances that contribute to its failure or fuccess. On these particulars, however, as well as every other refpe&ting fo remarkable an experiment, the Author observes the moft profound filence. He afterwards, indeed, diversifies it, only by making a man's body a part of the circuit; and then adds an obfervation which he needed not to have made, 'had he related all that he knew concerning this matter*.

If, says 'he, the operator does not receive the shock in his arms, notwithstanding the intervening of the glafs panë, 'I am much deceived: adding," If these experiments will stand the test of a fair examination, is it poffible not to conclude, that glafs is permeable to the electric fluid ?'

In our Review of this performance, our remarks are neceffarily confined to fuch parts of it as do not require the aftance of plates. Even under this restriction, we meet with abundant matter for animadverfion. The following experiment is produced by the Author, with a view to Mew the insufficiency of the Franklinian theory to account for the principle upon which the Leyden vial acts. In our apprehenfion, it only fhews, that the Author has not fufficiently studied the theory which he attempts to demolifh ; without fubftituting a better, or any other, in its room.

• Take two jars, and charge them by their knobs, at the poo sitive conductor. While they are standing with their knobs in contact with the conductor, and at some distance from each other, form a communication between the outside of one of the jars, and the infide of both of them (for the conductor connecting the two jars together by their knobs, their internal surfaces become as one), and there will be a fpark, a fhock, and a

* We entertain not the least doubt of Mr. Lyon's veracity; but fuppose that he may have been deceived; and that the electric macter may have passed over the surface of the glass. If, however, he will transmit to our Edicor any further explanation of this fingular experiment, we shall take a pleasure in communicating his obferva tions to the Public, in our CORRESPONDENCE.

discharge

B 2

discharge of both the jars, notwithstanding the outside coatings are at a considerable distance from each other.

. If the charging of glass depends upon repelling as much of the electric fluid from one fide, as is condensed upon the other, and the discharging upon restoring the equilibrium ; then the external surface of one jar could not contain the electric Aụid condensed upon the internal surfaces of two jars. Besides, how is the equilibrium restored to that jar which has no communication with the infide? The jars are both apparently in the fame state after the discharge is made, as they were before they were charged.'

It is sufficient to ask the Author how it is possible---suppofing both jars to be placed on the table, or their outsides to communicate with the earth-that the second jar, or that to the outside of which the discharging rod is not applied, can fail of being discharged; when, at the time of the discharge, the discharging rod forms a communication between its infide coating and the earth. It would be strange, indeed, if the second jar were not discharged, when its inlide coating communicates with the prime conductor; and when one end of the discharging rod touches the prime conductor, while its other end touches the outside coating of the first jar, which stands on the table, and consequently communicates with the earth. Were the jars insulated, a coinplete discharge would not take place.

We forgot to mention, in their proper place, some particular cases which the Author produces at pag. 58, 59, &c. to fhew, that glass is permeable to the electric fluid; which are all very eafily to be accounted for on the Franklinian fyftem. With respect to the remark at pag. 61, we need only to observe, granting the facts, that it is well known, that, when a vial is highly charged, and the electrization continued, and vigorous, the electric Auid will pass over the surface of glass and other electrics, how dry foever, to a confiderable distance. The Author himself, in the 2d experiment related in this work, shews that it will pass to the distance of four feet.

The Author, fuppofing that he has proved the permeability of glass to the electric Auid, and consequently that he has overturned the Franklinian theory, proceeds, in his roth chapter, to give us ' An Analysis of the Leyden Vial.' But though, in the course of this chapter, he very frequently gives the Reader hints, that he is explaining the mysteries of this wonderful bottle, by a better hypothesis; we have more than once studied it from beginning to end, without being able to discover in it any thing that carries the most distant appearance of a satisfactory analysis. We here meet indeed with several experiments which, so far as we understand them, do not tend to throw the least additional light on the Leyden vial: much less are they

adapted

S adapted to overturn Dr. Franklin's simple and luminous explapation of its fingular properties.

The Author, indeed, here, as well as elsewhere, carries on an analogy between electricity and magnetism, as others have done before him; and ascribes a kind of polar virtue to the particles of the electric matter. Electrical attractions and repulsions have. an undoubted resemblance to certain phenomena of magnetism: but the Reader, who is kept in continual expectation that the mysteries of the Leyden vial are about to be explained by the Author's polar system, arrives at the end of the chapter, and afterwards at the end of the book, without learning how the polar virtues of the electric matter are employed, either in the charging or in the discharging of the vial. And yet, perhaps, it might not be difficult, on this head, to frame a plausible hypothefis, on the suppofition that the electric particles are endowed with poles : but not without adopting the Franklinian doctrine of the impermeability of glass, as an indispensable, poftulatum. The Author, however, has not only given up the advantage he’might have derived from the adoption of this principle; but has taken pains to confute it, and has accordingly, as might be expected, left the Leyden vial as big with mystery and contradiction as it stood above 30 years ago; when Dr. Franklin explained all its seeming anomalies, by a simple hypothesis founded on this very principle. In short, the Author, by maintaining the permeability of glass, has undertaken to thew, how a vessel becomes the better adapted to receive and contain a Auid poured into it, because it is full of holes, which permit just as much of the fluid to run out, or through its fides, as is poured into it; whereas, if the vessel were perfectly found, or impenetrable, it would neither receive or retain a drop of it :and his fuccess is such as' might be expected in so hopeful an enterprize.

The greater part of the Author's experiments requires the having a recourse to the two plates which he has given; in which is delineated a most complex apparatus, consisting of such a variety of members, that in some cases, it is not very easy to comprehend their structure, or the purport for which they are put together. As a specimeni however of such of his experiments as do not require the affistance of figures, we shall transcribe the first of a particular fets which, • as perhaps having novelty to recoinmend them,' he recites' for the entertainment of the prace tical electrician, without taking any notice of the design for which they were made.'

• Fill a coated jar with boiling water as high as the top of the infide coating, and place it in a glass vesel, and then fill the vessel with boiling water, till it rises to a level with the water in the coated jar. Fill another jar of glass, to the same

B 3

height

« AnteriorContinuar »