to them; so 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 stroke in this cafe: as we think his estimate 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 whatsoever; and fince a returning ftroke, when produced by the fudden removal of even the weak elaftic electrical preffure of the electrical atmosphere of a charged prime conductor, may be extremely strong, 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 ftrength 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 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 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 fhould deftroy or even injure him. In the experiment above described, 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 muft neceffarily re-pafs through his body, to arrive at that conductor. To render the case somewhat parallel, in natural electricity, the man's body must be fo peculiarly circumstanced, fuppofing him to be in a house, that the electric matter which 1 We suppose 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 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 cafe 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 distant explosion: and that this quantity is not ufually very large may inferred from many confiderations. be 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 ftate 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 hoes 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 ftruck with lightning. He adds, if a man walking out of doors were to be killed by a returning ftroke; the electrical fire would rufh 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 circumstances attending the cafe minutely ascertained: 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 froke 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 thunderstorm, 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 flighter degrees, would be familiar; and fcarce a great thunderftorm must have occurred, in which one perfon or another must not, at the inftant of an explosion, have felt the effects of the returning stroke, in fome degree or other-from that of a vio lent 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 spot where the explosion took place. The Author has been aware of this objection, which he proposes, and endeavours to remove but his anfwer to it amounts to little more than what has been already quoted from him; that is, to a fimple estimate 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 observed, 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 fmall, quantity of electric matter. We have been induced to difcuts 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 stroke 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 infant 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 stroke' (or spark) 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 harp 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 firoke, but merely its existence; which we do not conteft, holds holds out a new and, in our opinion, groundless subject of terror to those 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 believed, would never think themselves in fecurity while a thundercloud appeared in fight, unlefs fheltered in a houfe furnished with proper conductors:-for we fhould 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 ftroke whatever, as well as of the main ftroke. Indeed various parts of this work, befides thofe immediately appropriated to the subject, 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 difcuffes 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 fhall 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 should be preffed into actual contact by means of nuts and fcrews; with a thin piece of sheet lead between the shoulders 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 thould 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 bear an extremely fmall proportion to its height; for instance that of one to forty. 7thly, That it be extremely prominent;'-that is, 8, 10, or 15 feet at leaft above the highest parts of the building. The Author lays great ftrefs on this circunftance; in consequence of the law above mentioned, deduced by him from his experiments relating to electric atmospheres. According to this law, the denfity of an electric atmosphere (the negative atmosphere, for inftance, of the roof of a houfe, &c. while a pofitively charged cloud hangs over it) diminishes in the inverse ratio of the fquare of the distance from the furface of the body to which that atmofphere belongs. Accordingly, if the rod project twelve feet into this atmosphere, it will reach to a part of it four times lefs dense than if the rod projected only to half that distance, or fix feet; and to a part one hundred and forty four times rarer, than if it projected only one foot. 8thly, That each rod be carried, in the fhorteft convenient direction, from the point at its upper end, to the common stock.' 9thly, That there be neither large nor prominent bodies of metal upon the top of the building propofed to be fecured, but fuch as are connected with the conductor, by fome proper metallic communication.' Iothly, That there be a fufficient number of high and pointed rods.'-On edifices of great importance, efpecially magazines of gunpowder, the Author thinks thefe ought never to be above 40 or 50 feet afunder. 11thly, That every part of the rods be very fubftantially erected.' The Author declares that he has never been able to hear of a fingle instance, nor does he believe that any can be produced, of an high, tapering, and acutely pointed metallic conductor having ever, in any country, been ftruck by lightning; if it had all the neceffary requifites above mentioned, especially the fecond and fourth. One of the new principles contained in this work, and which the Author conceives to be as important as it is new, is, that it is the electricity itself, contained in an electrical atmosphere, which ferves fuddenly to conduct, to a given diftance, any given electrical charge.'-One illuftration of this principle is, that a charged prime conductor will not, for instance, ftrike into a ball prefented to it, at its greatest striking distance, till it had been previously made to ftrike upon the ball at fome fmaller distance: the ball being afterwards gradually removed from it, till it reached the greateft ftriking distance. He fuppofes that, in the previous horter explosions, the air lying in the path of the sparks being electrified by them, in their paffage through it, becomes a better |