tance of five or fix feet from both of them. This returning ftroke is evidently occafioned by the fudden re-entrance of the electric fire naturally belonging to his body and to the fecond conductor, which had before been expelled from them by the action of the charged prime conductor upon them; and which returns to its former place, the inftant that action or clastic preffure ceafes. The Author fhews that there can be no reason to fuppofe that the electrical discharge from the prime conductor fhould, in this experiment, divide itself at the inftant of the explosion, and go different ways; so as to strike the second conductor and infulated perfon in this manner, and at such a diftance from it.

When the fecond conductor and the infulated person are placed in the denfest part of the electrical atmosphere of the prime conductor, or just beyond the ftriking distance; the effects are ftill more confiderable: the returning froke being extremely fevere and pungent, and appearing confiderably fharper than even the main ftroke itfelf, received directly from the prime conductor. This circumftance the Author alleges as an unanfwerable proof that the effect which he calls the returning ftroke was not produced by the main ftroke being any wife divided at the time of the explofion, fince no effect can ever be greater than the caufe by which it is immediately produced.'-Having taken the returning ftroke eight or ten times one morning, he felt a confiderable degree of pain acrofs his cheft during the whole evening, and a difagreeable fenfation in his arms and wrifts all the next day.

We come now to the application of this experiment, and of the doctrine deduced from it, to what paffes in natural electricity, or during a thunderstorm; in which there is reason to expect fimilar effects, but on a larger fcale :-a fcale fo large indeed, according to the Author's reprefentation, that perfons and animals may be deftroyed,-and particular parts of buildings may be confiderably damaged, by an electrical returning Stroke, occafioned even by fome very diftant explofion from a thundercloud;'-poffibly at the diftance of a mile or more.

It is certainly eafy to conceive that a charged extenfive thundercloud must be productive of effects fimilar to those produced by the Author's prime conductor. Like it, while it continues charged, it will, by the fuperinduced elastic electrical preffure' of its atmosphere-to ufe the Author's own expreffiondrive into the earth a part of the electric fluid naturally belonging to the bodies which are within the reach of its widely extended atmosphere; and which will therefore become negatively electrical. This portion too of their electric fire, as in the artificial experiments, will, on the explofion of the cloud, at a diftance, and the ceflation of its action upon them, fuddenly return

to them; fo as to produce an equilibrium, and reftore them to their natural state.

We cannot however agree with the ingenious Author, with refpect to the greatness of the effects, or of the danger, to be apprehended from the returning ftroke in this cafe: as we think his eftimate is grounded on an erroneous foundation. Since, fays he, the electrical density of the electrical atmosphere of a thundercloud, is fo immenfe, when compared to the electrical denfity of the electrical atmosphere of any prime conductor, charged by means of any electrical apparatus whatsoever; and fince a returning ftroke, when produced by the fudden removal of even the weak elastic electrical preffure of the electrical atmosphere of a charged prime conductor, may be extremely ftrong, as we have feen above: it is mathematically evident, that, when a returning ftroke comes to be produced by the fudden removal of the very strong elaftic electrical preffure of the electrical atmosphere of a thundercloud powerfully charged; the ftrength of fuch a returning stroke must be enormous.'

If indeed the quantity of electric fluid naturally contained in the body of a man, for inftance, were immenfe, or indefinite, the Author's estimate between the effects producible by a cloud, and those caused by a prime conductor, might be admitted. But furely an electrified cloud,-how great foever may be its extent, and the height of its charge, when compared with the extent and charge of a prime conductor-cannot expel from a man's body (or any other body) more than the natural quantity of electricity which it contains. On the fudden removal therefore of the preffure by which this natural quantity had been expelled, in confequence of the explosion of the cloud into the earth; no more (at the utmost) than his whole natural stock of electricity can re-enter his body t. But we have no reason to suppose that this quantity is fo great, as that its fudden reentrance into his body should destroy or even injure him.

In the experiment above defcribed, the infulated perfon receives into his body, at the instant of the returning ftroke, not only all that portion of his own natural electric fire which had been expelled from it; but likewife tranfmits through it, at the fame inftant, in confequence of his peculiar fituation, all the electric fire of which the large fecond conductor had been robbed; and which must neceffarily re-pass through his body, to arrive at that conductor. To render the cafe fomewhat parallel, in natu ral electricity, the man's body must be so peculiarly circumstanced, supposing him to be in a house, that the electric matter which

We fuppofe the perfon not to be fo fituated, that the returning fire of other bodies must neceffarily pass through his body.

Ff4

has

has been expelled from the houfe into the earth, by the preffure of an extenfive thundercloud, could not return back into the building, on the explofion of the cloud at a diftance, without paffing through his body: a cafe not likely to happen, unlefs the house were infulated (like the fecond conductor in the preceding experiment), and his body became the channel through which alone the houfe could have its electric matter restored to it it appears much more probable that the electric matter returns to the house through the fame channels by which it before infenfibly paffed out, and with equal filence, though more fuddenly.

In the cafe of a man who is abroad, and in an open field, during the time of an explosion ;-as he is unconnected with other maffes of matter above him, no more than the precife quantity of electric fire, which had been before expelled from his body, will fuddenly return into it at the inftant of a distant explofion and that this quantity is not ufually very large may be inferred from many confiderations.

:

When a person standing on the ground holds a pair of Mr. Canton's balls in his hand, while a highly charged thundercloud is fufpended over his head; the angle made by the balls indicates the electrical state of that perfon, or the quantity of natural electricity of which his body is at that time deprived, by the action of the (pofitively) charged cloud hanging over him. But we have never feen the repulfion of the balls fo confiderable, as to furnish any juft apprehenfions that the return of his natural electric matter, however fudden, could be attended with injury to him: nor would he be fenfible of any commotion on the balls fuddenly coming together; though a fpark might undoubtedly be perceived, at that inftant, were he infulated, and placed in the fame manner with the Author, when he tried the above related experiment.

The Author nevertheless obferves, that there have been inftances of perfons, who have been killed by natural electricity, having been found with their shoes torn, and with their feet damaged by the electrical fire; but who have not had, over their whole body, any other apparent marks of having been struck with lightning.' He adds, if a man walking out of doors were to be killed by a returning ftroke; the electrical fire would rush into that man's body through his feet, and his feet only; which would not be the cafe, were he to be killed by any main Stroke of explofion, either pofitive or negative.'

It would be no difficult task, we think, to account for these appearances in a different manner; were all the circumstances attending the cafe minutely afcertained: but without interrogating the dead on this fubject, we may more fatisfactorily appeal

to

to the experience of the living *, to fhew that though the returning ftroke muft take place, in all thunderstorms, in fome degree or other; yet it is not of that alarming magnitude which the Author afcribes to it. If in any particular thunderftorm, a man in the open fields could be killed, at the inftant of a diftant explosion, merely by the return of his own electric fire, which had before been driven out of his body: furely numerous obfervations of perfons who had experienced the returning ftroke, in fighter degrees, would be familiar; and scarce a great thunderftorm must have occurred, in which one perfon or another must not, at the inftant of an explofion, have felt the effects of the returning ftroke, in fome degree or other-from that of a violent concuffion, to that of a flight and almoft imperceptible pulfation. But no obfervations of this kind are known to us; nor have we ever heard of any perfons experiencing any kind of electrical commotion in a thunderstorm, except fuch as have either been directly ftruck, or have happened to be in the very near neighbourhood of the fpot where the explofion took place.

The Author has been aware of this objection, which he propofes, and endeavours to remove: but his answer to it amounts to little more than what has been already quoted from him; that is, to a fimple eftimate of the enormous difference between the electrical denfity, or the elaftic electrical preffure, of the atmosphere of an extenfive thundercloud, and that of a charged prime conductor. We have already obferved, that this is not the proper method of eftimating their different effects, when thefe two caufes, how unequal foever in power, are confidered as exerting that power on bodies containing a limited, and comparatively small, quantity of electric matter.

We have been induced to difcufs this fubject thus particularly, with a view to quiet the minds of the timorous; as the Author's extenfion of his principles, refpecting the returning ftroke in artificial electricity, to what paffes in natural electricity,

* The Author does indeed produce a living evidence, in the cafe of a perfon at Vienna, who, he has been credibly informed, received an electrical shock, by having held one hand accidentally in contact with an interrupted metallic conducting rod, at the inftant that a thundercloud exploded at the distance, as was conjectured, of above half an English mile. He likewife obferves, that a very strong, bright, and fudden froke' (or fpark) of electrical fire has been feen by feveral electricians, to pafs in the interval, or interruption, purpofely left in the conducting rod of a house, at the inftant of a diftant explosion; and when it was fully proved, by the sharp point of the conductor not being melted, or even tinged,' that the conductor itself had not been ftruck.-Thefe obfervations, however, do not by any means prove the magnitude, or danger, of the returning ftroke, but merely its exiflence; which we do not conteft.

holds

holds out a new and, in our opinion, groundless subject of terror to thofe who, in the midst of their apprehenfions, have hitherto only dreaded the effects of a thunderstorm when it made near approaches to them; but who, if this doctrine were beJieved, would never think themselves in fecurity while a thundercloud appeared in fight, uniefs fheltered in a houfe furnished with proper conductors:-for we should not omit to remark, that a fubfequent obfervation tends to diminish their fears, by fhewing that high and pointed conductors tend to fecure both perfons and buildings, against the various effects of any returning firoke whatever, as well as of the main ftroke.

Indeed various parts of this work, befides thofe immediately appropriated to the fubject, tend to prove the utility of high and pointed conductors, in preference to thofe which terminate in a ball, or rounded end. Towards the end of the performance, the Author difcufles this matter very particularly; and enumerates the neceffary requifites' in erecting them, in number eleven; to every one of which, though we have taken the liberty to differ from him on another fubject, we readily fubfcribe. As this matter is of a popular nature, and on a fubject generally interefting, we shall tranfcribe this lift; adding a fhort explanation to particular articles.-Thefe requifites (fays the Author) are eleven in number:

Ift, That the rod be made of fuch fubftances, as are, in their nature, the best conductors of electricity.'

2dly, That the rod be uninterrupted, and perfectly continuous.' -This is a very material circumftance. One intire piece of metal cannot perhaps be had: but it is not fufficient that the rods, of which the conductor confifts, be fenfibly in contact. They fhould be preffed into actual contact by means of nuts and fcrews; with a thin piece of fheet lead between the fhoulders of the joints.

3dly, That it be of a fufficient thickness.'—A copper rod half an inch fquare, or an iron rod one inch fquare, or one of lead two inches fquare, are thought fully fufficient by the Author.

4thly, That it be perfectly connected with the common ftock.'-That is, it fhould be carried deep into the earth, which is frequently dry near the furface; and then continued in a horizontal direction, fo as to have the farther extremity dipped, fhould this be practicable, into water, at the diftance of 10 yards or more from the foundation.

5thly, That the upper extremity of the rod be as acutely pointed as poffible.'-This termination fhould be of copper; or rather a very fine and exceedingly acute needle of gold should be employed, which will not materially add to the expence.

6thly, That it be very finely tapered :'-fo that the upper extremity may be a cone, the diameter of the bafe of which may

bear