posed to the escape of the fuperabundant electricity of the body, into that rare part of its electrical atmosphere into which the point projects. Among other illuftrations of this principle the Author produces the cafe of a pointed wire, placed between two round or prominent metallic bodies, with its point on a level with their furfaces. In this fituation, when prefented to an electrified body, it acts no longer as a point, or only in a very small degree because the denfe part of the electrical atmosphere of the two round bodies flows or is extended over it. The Author's fucceeding experiments fhew that an infulated fmooth body, a cylindrical conductor for inftance, immerged within the electrical atmosphere, but beyond the striking distance, of another body, which we shall suppose to be charged pofitively, is, at one and the fame time, in different parts of it, in aftate of three-fold electricity.' The end next to the charged body acquires negative electricity; and the farther end becomes pofitively electrified: while a certain part of the body, fomewhere between its two extremities, is in a natural, unelectrified, or neutral state: fo that the two contrary electricities exactly counterbalance each other in that part. The Author on this occafion employs geometrical reafoning, as well as experiments, to determine the precife place of this un-electrified point, or rather line, in a cylinder or other given body; and to demonftrate that the denfity of electrical atmospheres is inverfely as the fquare of the diftance from the electrified body. We scarce need to add, that if the body be not infulated, or have a communication with the earth, the whole of it will be in a negative ftate: a certain portion of its natural quantity of electricity being driven into the common mafs, by the pressure, repulfion, or other action, of the electric matter belonging to the charged prime conductor. The extensive and fruitful principle, on which this and the preceding effects depend, has frequently been explained or referred to in the course of our Journal; particularly, and very lately, in our Review for December laft, page 408; where it is noticed for the purpose of explaining the phenomena of the electrophorus. We take the more particular notice of it at prefent; as one of the Author's most remark able obfervations on the fubject of thunderstorms, and from which he draws fome very ftriking, indeed formidable, conclufions, is founded upon it. We allude to what the Author calls the electrical returning froke; by means of which, he alleges that, in a thunderstorm, * To avoid repetition, or circumlocution, we fhall, throughout the remainder of this Article, conftantly fuppofe the electrified body to be charged with positive electricity. the the most fatal effects may be produced, even at a vast distance from the place where the lightning falls. This obfervation appears to be of fo much importance, that we fhall endeavour to give as clear an idea of the experiments on which it is founded, as can be conveyed by us, without the use of plates: not confining ourselves to any particular experiment; but relating fuch material circumstances common to them all, as may best convey the Author's meaning in the feweft words. We ought to premife that the Author ufed a very powerful machine, made by Mr. Nairne; the prime conductor of which (fix feet long, by one foot diameter) would generally, when the weather was favourable, ftrike into a brafs ball connected with the earth, to the diftance of eighteen inches, or more. In the following account this brafs ball, which we fhall call A, is fuppofed to be conftantly placed at the striking diftance; fo that the prime conductor, the inftant that it becomes fully charged, explodes into it. Another large conductor, which we fhall call the fecond conductor, is fufpended, in a perfectly infulated ftate, farther from the prime conductor than the striking distance, but within its electrical atmosphere;-at the diftance of fix feet, for inftance. A perfon standing on an infulating ftool touches this fecond conductor very lightly with a finger of his right hand; while, with a finger of his left hand, he communicates with the earth, by touching very lightly a fecond brass ball fixed at the top of a metallic ftand, on the floor, and which we fhall call B. While the prime conductor is receiving its electricity, sparks pafs (at leaft if the distance between the two conductors is not too great) from the fecond conductor to the infulated perfon's right hand; while fimilar and fimultaneous fparks pass out from the finger of his left hand into the fecond metallic ball B, communicating with the earth. These fparks are part of the natural quantity of electric matter belonging to the fecond conductor, and to the infulated perfon; driven from them, into the earth, through the ball B, and its ftand, by the elaftic preffure or action of the electrical atmosphere of the prime conductor. The fecond conductor and the infulated person are hereby reduced to a negative state. At length however the prime conductor, having acquired its full charge, fuddenly ftrikes into the ball, A, of the first metallic ftand, placed for that purpose at the striking distance of 17 or 18 inches, The explosion being made, and the prime conductor fuddenly robbed of its electric atmosphere, its preffure or action on the fecond conductor, and on the infulated perfon, as fuddenly ceases; and the latter inftantly feels a smart returning froke, though he has no direct or vifible communication (except by the floor) either with the striking or ftruck body; and is placed at the dif Ff3 tance 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 elastic preffure ceases. The Author fhews that there can be no reason to fuppofe that the electrical discharge from the prime con ductor fhould, in this experiment, divide itself at the inftant of the explufion, and go different ways; fo as to ftrike the second conductor and infulated perfon in this manner, and at fuch a diftance from it. When the fecond conductor and the infulated perfon are placed in the denfeft part of the electrical atmosphere of the prime conductor, or just beyond the ftriking diftance; the effects are ftill more confiderable: the returning ftroke 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 firoke was not produced by the main firoke being any wife divided at the time of the explosion, fince no effect can ever be greater than the cause 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 scale fo large indeed, according to the Author's reprefentation, that persons and animals may be deftroyed,-and particular parts of buildings may be confiderably damaged, by an electrical returning Stroke, occationed even by fome very diftant explosion 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 thofe produced by the Author's prime conductor. Like it, while it continues charged, it will, by the fuperinduced claftic electrical pref fure' of its atmofphere-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, wil!, on the explcfion of the cloud, at a diftance, and the ceffation of its action upon them, fuddenly return to them; fo as to produce an equilibrium, and restore them to their natural state, We cannot however agree with the ingenious Author, with respect 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 denfity 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 what foever; and fince a returning ftroke, when produced by the fudden removal of even the weak elaftic electrical preffure of the electrical atmofphere of a charged prime conductor, may be extremely frong, as we have seen 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 strength of fuch a returning ftroke 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 eftimate between the effects producible by a cloud, and thofe caufed 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 utmoft) than his whole natural flock of electricity can re-enter his body . But we have no reason to fuppofe that this quantity is fo great, as that its fudden reentrance into his body should deftroy or even injure him. In the experiment above defcribed, the infulated person receives into his body, at the inftant 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 natural electricity, the man's body must be so peculiarly circumstanced, fuppofing him to be in a houfe, that the electric matter which ↑ We fuppofe the perfon not to be fo fituated, that the returning fire of other bodies must neceffarily pafs through his body. has Ff4 has been expelled from the houfe into the earth, by the pressure of an extensive thundercloud, could not return back into the building, on the explosion of the cloud at a distance, without paffing through his body: a cafe not likely to happen, unless the house were infulated (like the second conductor in the preceding experiment), and his body became the channel through which alone the house 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 case of a man who is abroad, and in an open field, during the time of an explofion ;-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 diftant 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 suspended 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 spark 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 fhoes 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 firoke of explosion, either pofitive or negative.' It would be no difficult task, we think, to account for these appearances in a different manner; were all the circumftances attending the cafe minutely ascertained: but without interrogating the dead on this fubject, we may more fatisfactorily appeal to |