Dr. Milne's zeal against infidels and infidelity is fo great, that he could not avoid a fort of a back-hand ftroke at Mr. Hume, and his manner of quitting the world. He will boast to the last moments (fays the Preacher) of a pretended strength of mind which fhall flatter his vanity; incline to feem fuperior to vulgar errors, to brave the authority of heaven, and view the uncertainty of an hereafter with a fixed and tranquil eye; leave to the fpectators the dreadful pleasure of a witticism at the expence of his eternal falvation, and talk jocularly of Styx and Charon.” (Vid. Serm. On the Deceitfulnefs of Sin, p. 216. comp. with Dr. Adam Smith's Letter to William Strahan, Efq; affixed to Mr. Hume's Life.) We fhall produce one fpecimen more of the Preacher's zeal ; and it will ferve as a farther fpecimen of his happy talent at antithefis. Would you take thofe for your models whofe names offer themselves with horror to remembrance, the Vaninis, the Spinofas, the Woolftons, the Voltaires? or the Now, gentle Reader, doft thou not expect fome modern champion of the Chriflian church to figure in the contraft?-the Pafcals, the Boyles, the Newtons, the Lockes, the Lytteltons? -Thou art miftaken! Dr. Milne oppofes to the Spinofas, the Woolftons and the Voltaires- the Abrahams, the Jofephs, the Jobs, the Elijahs, the Daniels, the apoftolical men, who fhone as lights in the world. Maintain (fays he) if you can this parallel.It is not our bufinefs, nor the bufinefs of any one's but the Doctor's, to maintain fuch a parallel; and it will require more ingenuity than he is poffeffed of to maintain it with any grace. Dr. Milne, and the partial friends who perfuaded him to commit his compofitions to the inspection of the public,' will certainly accufe us of great severity and ill-nature in treating him with fuch freedom as we have in the preceding remarks. But when we think we have difcharged an honeft, though harsh and ungrateful duty; and when we know that we have done it without the flighteft perfonal prejudice against the Author, or even the most diftant knowledge of the man, any farther than he hath made himself known to us by his publications, we shall acquit ourselves to our own confciences, and confider every fplenetic reflection from partiality and disappointment as a thing of course. We confider Dr. Milne as a most dangerous and corrupt model for our young divines-who are too eafily captivated by the charms of a falfe and fpecious eloquence, to the neglect, and perhaps the contempt, of those words of truth and foberness, which aim more at the conviction of the judgment than at the inflammation of the paffions; and gain by a calm and lafting effect, what they miss by sudden and violent emotions. ART. ART. IV. Principles of Elearicity, containing divers new Theorems and Experiments, together with an Analysis of the fuperior Advan→ tages of high and pointed Conductors, &c. By Charles Viscount Mahon, F. R. S. 4to. 10. 6d. Boards. Elmfly. 1779. TH HOUGH the ingenious and noble Author of this per formance profeffes to establish in it the fundamental laws of Electricity; the prefent is not an elementary treatife of that Icience. The reader is accordingly fuppofed to be acquainted with the common experiments, and the general properties of electricity, which have been already established by others. The Author firft treats of Electric Atmospheres; and endeavours to fhew that they are conftituted of the particles of air furrounding the electrified body. If, for inftance, the body be pofitively electrified, he maintains that it will depofit, upon all the particles of air that furround it, and come fucceffively in contact with it, a proportional part of its fuperabundant electricity: fo that they will become likewife pofitively electrified, and form a pofitively electrified atmosphere *. The fame reasoning is applied, mutatis mutandis, to negatively electrified bodies, and their negative atmospheres. From this principle, and the obfervation that the density of an electrical atmosphere diminishes, in a certain ratio, as the diftance from the electrified body increases, as well as from other confiderations, the Author undertakes to affign the caufe, why an electrified body, to which a projecting point is affixed, parts with, or receives, electricity more readily than a fmooth cylindrical or globular body:-Because the fuperabundant electricity of the body, which we will suppose to be pofitively electrified, and which, in all cafes, tends to quit it, will, when a point is affixed to it, meet with lefs refiftance to its efcape; as the point projects beyond the denfe part of the electrical atmosphere of the body, into the rarer and, confequently, more unrefifting part of that atmosphere. But the escape of the electric matter from any part of a smooth cylindrical body, pofitively electrified, is prevented or impeded; because every part of its furface is in contact with the denfest part of its own strongly refifting electric atmosphere. The furface too of the point being extremely fmall, the lefs will be the resistance op * We wonder that the Author should take no notice of those ob. fervations of Dr. Franklin, that feem to militate against this doctrine; particularly his experiment, in which a large electrified cork ball, fixed to the end of a filk ftring, was whirled fwiftly round a hundred times in the air, like a fling; without fuftaining any fenfible lofs of electricity, after having paffed through 800 yards of air. See his Experiments and Obfervations on Electricity, &c. Letter VI. Ff2 pofed 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 instance, immerged within the electrical atmosphere, but beyond the ftriking distance, of another body, which we fhall fuppofe 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 reasoning, 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 distance from the electrified body. We fcarce 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 state: a certain portion of its natural quantity of electricity being driven into the common mafs, by the preffure, repulfion, or other action, of the electric matter belonging to the charged prime conductor. The extenfive and fruitful principle, on which this and the preceding effects depend, has frequently been explained or referred to in the courfe of our Journal; particularly, and very lately, in our Review for December last, 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 striking, indeed formidable, conclufions, is founded upon it. We allude to what the Author calls the electrical returning Stroke' by means of which, he alleges that, in a thunderstorm, To avoid repetition, or circumlocution, we fhall, throughout the remainder of this Article, contantly fuppofe the electrified body to be charged with pofitive electricity. the the most fatal effects may be produced, even at a vast diflance from the place where the lightning falls. This obfervation appears to be of fo much importance, that we shall 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 circumftances common to them all, as may beft convey the Author's meaning in the fewest words. We ought to premife that the Author used 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 friking distance, but within its electrical atmosphere;-at the diftance of fix feet, for instance. A perfon ftanding 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 brafs 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, fparks pafs (at least if the diftance between the two conductors is not too great) from the fecond conductor to the infulated perfon's right hand; while fimilar and fimultaneous fparks pafs out from the finger of his left hand into the fecond metallic ball B, communicating with the earth. Thefe 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 perfon 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 firiking distance of 17 or 18 inches, The explofion 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 ftroke, though he has no direct or visible communication (except by the floor) either with the friking 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 elaftic preffure ceases. The Author fhews that there can be no reason to fuppofe that the electrical difcharge from the prime conductor should, in this experiment, divide itfelf at the instant of the explosion, and go different ways; fo as to strike the second conductor and infulated perfon in this manner, and at such a diftance from it. 6 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 ftroke being extremely fevere and pungent, and appearing confiderably fharper than even the main ftroke itself, received directly from the prime conductor. This circumftance the Author alleges as fwerable proof that the effect which he calls the returning stroke 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 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 across 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 representation, that persons and animals may be deftroyed,--and particular parts of buildings may be confiderably damaged, by an electrical returning ftroke, occafioned 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 those preduced 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 explosion of the cloud, at a diftance, and the ceffation of its action upon them, fuddenly return |