be overbalanced, or more than compenfated for, by the exhaufting power of the point. In Mr. Nairne's three laft experiments above mentioned, when the conductor, variously terminated, was made to fwing, even with great rapidity, under a large electrified conductor; a rounded termination was ftruck, with an equal charge, at a much greater distance than a pointed extremity. No explofion enfued, when the point paffed at a greater diftance than I inch and ths. A ballths of an inch in diameter, was ftruck at the distance of 2 inches and th; and a larger ball of 1 inch and ths diameter, received a ftroke at the diftance of 15 inches *.

Speaking of pointed conductors, at the end of the article, the Author owns, that if by operating upon a quantity of electricity too fmall in itfelf to do mifchief, they prevent its grow ing to a great and dangerous quantity; this would, as far as it goes, be a very confiderable advantage.' He adds, however, that pointed conductors afford no protection where the danger is great and imminent, and only obviate that which is diftant and problematical; and that these laft are not the cafes against which we principally wish to provide.'

Paffing over the cafe above difcuffed, where a very great charge prefents itself, as it were inftantaneously over a pointed conductor; there undoubtedly occur many cafes in which the cloud, A, for inftance, fufpended over a building, receives fucceffive charges from another cloud, B; and that, probably, from the cloud, C; none of which, fingly, are fufficient to enable the cloud, A, to ftrike into the building: though two or three fuch fucceffive charges might load it fufficiently for that purpose. In this cafe, it cannot be denied, that the continued action of the point on the cloud, A, during the intervals between the explofions, may prevent its ever acquiring fuch a

We fhould obferve, that the fingular difappearance and re-appearance of the fparks, on gradually removing the fmall conductor from the prime conductor, above noticed at the end of Mr. Nairne's article, occurred likewife in the two first of these cafes: but in the third, where the large ball was ufed, it was ftruck uninterruptedly, till it was removed to the distance of 16 inches.

+ Dr. Mufgrave has furely expreffed this too loosely. He cannot mean, that pointed conductors afford no protection to a building, under thefe circumstances; but only that they are more liable to be ftruck, on certain occafions, than blunt conductors. Either a pointed or a blunt conductor may be faid to afford protection to a building, although they fhould be ftruck by the lightning; as little doubt can now be entertained, that either of them will tranfmit it fafely to the earth, provided that they are made of a fufficient fize, and all other circumftances be attended to that are known to facilitate the paffage of the electric matter to the earth.

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quantity

quantity of electric matter, as to produce an explosion. The point, therefore, will afford protection in this cafe, where the danger is indeed, at first, fmall and problematical; but would become great and imminent, were the point taken away.

Article 38. On the Ufe of an Amalgam of Zinc, for the Purpose of electrical Excitation, &c. By Bryant Higgins, M. Ď.

&c.

This Amalgam, as we have already experienced, greatly exceeds any other that we have tried; and particularly, does not require fuch frequent application, as thofe made with tin, bifmuth, &c. It confifts of zinc, combined with four times its weight of quickfilver. To this amalgam fhould be added, though Dr. Higgins is filent on the fubject, a very small quantity of wax and tallow.-When the cylinder is become foul, the Doctor recommends the use of a piece of the dry skin of the dog fish, applied to it while it is turned round.

Article 44. New Experiments upon the Leyden Phial, refpecting the Termination of Conductors. By Benjamin Wilfon, Esq; F. R. S.

Thefe experiments were formerly published, at the end of Mr. Wilfon's account of the experiments he made at the Pantheon. They are brought to fhew that, on the difcharge of an electrified jar (that is, in the cafe of an inftantaneous explofion, where a point has not time to act upon the electric matter), a point is ftruck at a greater diftance than a ball. The particular refults are given in four tables, figned by Dr. Lind, Mr. Cavallo, and Mr. Wilfon. The contrary refults of Mr. Henly are alcribed by the Author to his having ufed a chain, or an imperfect circuit of communication, inftead of a wire, in his experiments.

Article 47. A ready Way of lighting a Candle, by a very moderate Electric Spark. By John Ingenhoufz, M. D. F. R. S.

In this paper, Dr. Ingenhoufz teaches the electrical philofo pher a very expeditious and commodious way of lighting his taper, by means of an electric fpark from a small charged Leyden vial, that has only eight or ten inches of metallic coating. Round one of the extremities of a bent wire, fome loose cotton is wrapped, which is rolled in fome fine powder of white or yellow refin. While the other end is held in contact with the outward coating, this end is brought to the knob. The refin takes fire, and communicates its flame to the cotton, and both together burn long enough to light a candle. The fame effect may be produced by the farina Lycopodii, or by dipping the cotton in oil of turpentine; efpecially if a little pin duft be Sprinkled upon it; but in both thefe cafes the, charge muft be fomewhat greater.

Dd 4

In

In the night, a large charged jar, prepared in Mr. Cavallo's manner, and which will retain its charge a month, may be kept in readiness, as a magazine of electric fire; from which the little vial may be inftantly and repeatedly charged, for this purpose.

Article 48. Elettrical Experiments, to explain how far the Phenomena of the Electrophorus may be accounted for, by Dr. Franklin's Theory of pofitive and negative Electricity, &c. By John Ingenhoufz, M. D. F. R. S.

The theory by which Dr. Ingenhoufz juftly folves the most confiderable phenomena of that curious inftrument, the Electrophorus, was gradually difcovered, and fucceffively afcertained, by Mr. Canton, Dr. Franklin, and Meffrs. Wilke and Æpinus. We have formerly explained this doctrine at fome length, in our account of Dr. Prieftley's Hiftory of Electricity; [See Monthly Review, vol, xxxvii. October 1767, p. 250, &c.] where we have obferved, " that the electric fluid, when there is a redundancy of it in any body, repels the electric fluid in any other body, within its influence, and drives it into the remote parts, or quite out of the body, if there be any outlet for that purpofe; thereby reducing the body to a fitate contrary to its own, i. e. a negative one." The fame principle is applicable, mutatis mutandis, to a body negatively electrified. Referring the reader to Dr. Ingenhoufz's more minute investigation of this inftrument, we shall give the following fhorter account of its principal properties, correfponding nevertheless with his explanation, in our own words.

According to the abovementioned principle, fuppofing the refinous plate to have been pofitively electrified (which cafe admits of a fomewhat eafier illuftration), the excited plate acts upon the electric matter naturally contained in the brass plate, or moveable metallic coating, applied to it; fo as to expel a part of its natural quantity, when an opportunity is given it to escape from it, in the form of a fpark, at that part where a finger is applied to it. If the brass plate be now lifted up, by its infulating handle, it is found to be in a negative ftate; and on prefenting a finger to it, another spark appears, which now paffes towards it; and it accordingly receives back its natural share of electric fluid from the finger of the operator. On being replaced on the electrophorus, and again touched, it again parts with a portion of its natural quantity of electric fluid; which is again reftored to it, on lifting it up, and again prefenting the finger to it. This proces may be repeated for a great length of time, with scarce any perceptible diminution of the virtue of the refinous plate; which, in fact, does not part with any of its own electric matter to the brafs plate, but, on the contrary, only expels a part of that which naturally belongs to the latter; and which, on lift

ing it up, is repeatedly restored to it from the earth, through the finger of the perfon who makes the experiment.

The cafe, in fhort, is perfectly analogous to the instance we gave from M. De Cigna (in the part of our work above referred to); where an immenfe number of fparks may be fucceffively taken from, and given to, an infulated plate of lead, on prefenting an excited glafs tube (or filk ftocking) at fome distance from it, and touching it; and then withdrawing the tube, and again touching the plate, fucceffively. If the infulated metal plate of an electrophorus be applied to an excited glass plate, or to one that has been charged, and then discharged, as in the Leyden experiment (or even to an excited glass globe, which it touches in little more than a point), in the fame manner as it is used with the electrophorus; the fame appearances will be prefented.

The principal difference between the refinous and the vitreous electrophorus is, that in the former, the virtue is much more permanent than in the latter; because refinous fubftances are not fo liable to be affected by the humidity of the air; and poffibly, becaufe they poffefs a power of retaining the electricity which they have received from friction, or communication, much longer than vitreous fubftances, independent of this circumftance. M. De Volta has given his electrophorus the title of perpetual, and has confidered it as preferving a kind of vestal fire, and not improperly as it is certainly poffible, after only once exciting it by friction, to preferve its power indefinitely by collecting a fufficient number of the sparks, when they grow weak, into a small coated vial, and then imparting to the electrophorus its former activity, by only reftoring to it its own fire; by running the coating of the vial over its furface, while the knob is held in the hand.

A curious method of effecting the fame purpose is described in this paper; which confifts in employing two refinous plates, and transferring the metal plate alternately from one of them to the other, and touching it after it is placed upon them. By this method, both the refinous plates have their electricity quickly increased; and the metal plate returns from each quite overcharged, fo that Leyden vials may be charged by it so very Atrongly as to break them.

The fingular appearances prefented by the electrophorus, have been thought by fome electricians to be incompatible with Dr. Franklin's theory of electricity: but the preceding illuftration of the principal phenomena of that inftrument fhews, that they are perfectly confiftent with that fyftem. It is true however, that, when Dr. Franklin, by means of his theory, explained the phenomena of the Leyden vial, or a charged plate of glass; it was not fufpected that, after the circuit between the two coat

ings was completed, and a difcharge produced, the glass ftill retained a power, as we now find it does, of furnishing such a number of fparks (fimply by the alternate removal and re-application of one of its coatings, &c.) as is more than fufficient to charge another vial or plate repeatedly. This quality, poffeffed by excited electrics, after they have been charged, and then difcharged, particularly by thofe of the refinous kind, fill remains to be accounted for: unless it be alleged, that Father Beccaria has explained this property in his treatise on, what he has thought proper to call, the Electricitas Vindex; a fhort account of which will be found in our xlvth vol. 1771. Appendix, p. 555, and the page following [where, at line 12, the reader is defired to correct an erroneous transposition of the text and inftead of this it does, in the common manner, even after it has been discharged”—to read-" this it does, even after it has been discharged in the common manner."] Article 49. Obfervations and Experiments tending to confirm Dr. Ingenhoufz's Theory of the Electrophorus; and to fhew the Impermeability of Glafs to the Electric Fluid. By William Henly, F.R. S.

We do not find any thing new in thefe experiments, which are only diverfifications of others well known. Towards the end, the Author relates an experiment made by M. Lullin, of Geneva; which Mr. Henly confiders as a curious addition to the many others that have been made, to fhew the real direction of the electric matter, in the difcharge of the Leyden bottle. We have frequently made remarks on the inconclufiveness of the former experiments, made with this view, both by the Author and others. They all decifively prove the effential difference between the two electricities: but not one of them-not even the prefent-appears to us to afcertain with abfolute certainty, the real courfe in which the electric fluid is moving. In M. Lullin's experiment, on difcharging a Leyden vial, pofitively, or negatively, electrified, the true direction is fuppofed to be indicated by the light's appearing on the upper, or the under furface of a card; and by the fpot where a hole is made; in confequence of an interruption made in the electric circuit, between the extremities of two wires, that form the communication between the infide and outside of the vial; one of which wires terminates on the upper, and the other on the under furface of the card.

PAPERS relating to MEDICINE. Article 29. On the Antifeptic Regimen of the Natives of Ruffia. In a Letter from Matthew Guthrie, M. D. of Petersburgh, to Dr. Priestley, F. R. S.

No people upon earth are, perhaps, more expofed to the operation of thofe predifponent caufes, which terminate in the production of

the