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laft mentioned ball of the little conductor; whenever a fpark ftruck the other ball facing the great conductor, a fimilar fpark ftruck on the point. On gradually lowering the pointed wire, the Author found that the fpark would not ftrike it beyond fix inches; but that, nevertheless, at the diftance of nine inches or more, the point appeared luminous, and fparks continued to pass from the great conductor to the small one; fo that it was evident that the point ftill carried off the electric fire from the conductor. On removing the pointed wire, and placing in its ftead the wire with the knob at the top, he found that the sparks would strike the knob at the distance of nine inches; that is, half as far again as they would ftrike the point: the explofion likewife was confiderably louder and ftronger.
The inferences that may be drawn from this experiment will readily occur to every electrician, who will probably deduce fimilar conclufions from fome of the experiments related in the following Article. In the prefent cafe, as the Author very properly obferves, the pointed wire is placed in circumstances much more unfavourable to its operation, as a point,' or to what we may call its prefervative power, than a pointed conductor prefented to a cloud. The latter has evidently the advantage of acting on the electric atmosphere of the cloud all the time that it is making its approaches, and of gradually di minishing, in fome degree, the charge, before the cloud comes near enough to give the ftroke; which, in fome cafes, may poffibly be hereby prevented: whereas, in this experiment, matters are fo circumftanced, that the intire quantity of electric fluid is made to rush on the point almoft inftantaneoufly; fo that the latter has scarce any measurable portion of time wherein it can act, as a point, in diminishing the charge, before the whole falls upon it, as a conductor. Rapid however and momentary as the paffage of the electric matter is, through this fmall fpace, it appears to us that the point really does act upon it, even under this difadvantageous circumftance; fo as to weaken the explosion, at a certain diftance, and totally to prevent it, beyond that distance :-effects, which there is reafon to expect that it will, in fome degree, produce, when acting upon a larger fcale, or on the contents of a charged cloud. Article 18. Experiments concerning the different Efficacy of pointed
and blunted Rods, in fecuring Buildings against the Stroke of Lightning. By William Henley, F. R. S.
Thefe experiments were planned and executed by the Author, with a view to obtain the best information that he could procure, on the interefting queftion alluded to in the title of this Article. Though fome of the facts here mentioned are not unknown to electricians, who have drawn from them the
fame conclufions as the Author has done, in favour of pointed conductors; yet the greater part of the experiments are new and ingenioufly contrived. We fhall endeavour to give the fubftance of one or two of them, in fuch terms as may render our account intelligible, without the ufe of figures.
To the external conting of a large charged jar, which was infulued, and whole infide coating was in contact with the prime conductor, were connected two chains. To the extremity of one of them was fixed a sharp pointed wire, while the other terminated in a knob. Both these chains were likewise infulated, and lay parallel to, and five inches diftant from each other. A large copper ball (eight inches in diameter) fixed on an infulating ftand, was placed exactly at half an inch diftance both from the point and the knob. By means of an infulated difcharging rod, the Author conveyed the charge from the prime conductor to the large copper ball. By the previous difpofition of the two chains, &c. the charge of the jar had now two channels prefented to it, to convey it to the external coating. Of thefe two it preferred that which terminated in a knob; for it leaped, we are told, to the knob, and inftantly discharged the jar; rendering that chain which connected the knob with the jar very luminous. But no light could be perceived on the chain which proceeded from the point to the coating of the jar; though it is faid that particular attention was paid to that circumftance. In this inftance it appears that the accumulated electric matter ftruck the conductor terminating in a knob, while that which ended in a point, escaped; though it was at an equal diftance from the large copper ball, which, in this experiment, may be confidered as reprefenting an electrified cloud.
Further, the Author infulated three large charged jars, containing about 16 fquare feet of coated furface, and fixed to the outfide or bottom of them a wire terminating in a large knob. At the distance of one inch and a half from this knob he fixed and infulated the large copper ball abovementioned. Bringing as before, by means of his difcharging rod, the charge of the three jars upon the copper ball, it leaped from thence to the knob, and the jars were difcharged with a full and loud explofion. On moving the copper ball only one eighth of an inch further from the knob, no explosion happened. He then removed the wire with its knob, and put in its place another wire of the fame diameter and length, bnt nicely tapered to a point. At the diftance of one inch from this point he placed the large copper ball, and then applying the difcharging rod as before, the jars were difcharged, and the point melted a little. But removing the copper ball only one eighth of an inch farther from the point, the charge could not ftrike it; though much
of it was foon drawn off filently, or without any explosion, by the point as appeared by the falling of the index of the Au thor's electrometer.
Suppofing, as before, the large copper ball to represent an electrified cloud, charged equally high in both the preceding cafes; it appears that a conductor terminating in a knob was ftruck by it, with a violent explofion, at the diftance of one inch and a half: whereas a pointed conductor, placed three eighths of an inch nearer, was not ftruck at all; but carried off a great part of the electric matter without any explosion.
It has however been fuppofed by fome that points may attract the fragments of a loose cloud, and thereby invite a ftroke. That they are not likely to produce these effects may perhaps appear from the Author's laft experiment. Having procured a large bullock's bladder, which he gilded with leaf copper, be fufpended it by a filken ftring to a lender arm of wood, which turned freely, in a horizontal direction, on the point of a needle. Having given the bladder a ftrong spark from the knob of a charged bottle, he prefented to it a knob at the end of a brass rod, and found that the bladder would move towards it at the diftance of three inches, and when it had got within one inch of it, would throw off its electricity into it, in a spark nearly, if not quite, as large, as that which it had received from the vial. But on giving the bladder another strong spark from the vial, and presenting a pointed wire to it, it would not move towards the wire; and when the point of the latter was brought nearly in contact with it, no fpark was perceived; fcarce any fenfible quantity of electricity remaining in the bladder.
These and the Author's other experiments tend greatly to confirm Dr. Franklin's firft thoughts on this fubject; which were, that pointed bodies would indeed attract the electric matter, in the gradual filent way, at a greater diftance than knobs; but that the latter would, at ftill greater diftances, produce an explosion.
Article 17. Remarks on the Aurora Borealis. By Mr. Winn In a Letter to Dr. Franklin.
These remarks, fuppofing that the Author has not been mifled by a series of concurrent accidents, appear to be of importance in meteorology, and may be of confiderable ufe to the feaman; as they tend to give him fair notice of an approaching storm, and even indicate from what quarter it will come. The fubftance of the Author's obfervation is, that conftantly, at least in 23 inftances that have occurred fince he first made the remark, the appearance of the Aurora Borealis has been followed, within 24 or 30 hours, with hard gales, or a tempest at South or South-west, attended with hazy weather and small
rain. Mr. Winn exemplifies the advantages which may be derived from this piece of knowledge, by the navigator; efpecially when he is failing near coafts which tend Eaft and Weft, and more particularly in the British Channel; where he has repeatedly, and greatly to his advantage, availed himself of this new prognoftic.
The electric matter, which is now on very probable grounds fuppofed to be the cause of the Aurora Borealis, has fo intimate a connection with meteorology, or the various modifications of the atmosphere; that even on the footing of theory alone, there appear juft grounds to pay regard to the Author's obfervation, which deferves the attention of navigators and others; who having firft fully afcertained the general truth of the remark, may afterwards difcover thofe exceptions or varieties which may be produced by accidental and local circumftances.
In the 28th Article are continued the meteorological obfervations, annually made at Lyndon in Rutland, by T. Barker, Efq; during the year 1773.
In the 14th Article several circumftances are communicated by the Hon. Mr. Barrington, relating to a species or variety of the trout, in Ireland, and there called the Gillaroo trout; the peculiarity of which is, that the ftomach refembles the gizzard of a bird. In the 15th and 32d Articles, feveral anatomical obfervations on the ftructure of the ftomach of this fish are communicated by Mr. Henry Watfon, and Mr. Hunter. In No. 27, fome particulars are given of the Houfe-martin, by the Rev. Mr. Gilbert White.
The 29th Article contains fome curious obfervations, made by Mr. Hunter, on certain fingular communications which are found to fubfift, in birds, between the cavities of the lungs, and certain other cavities in the fleshy parts, as well as in the hollow bones of thefe animals. Thefe receptacles of air having never yet been fufficiently defcribed, or perhaps attended to, either by Anatomifts or Natural Hiftorians, the Author defcribes many of these aerial communications which he has obferved, and offers fome conjectures concerning the final cause of this peculiar mechanifm. The difcovery of this caufe appears to be a matter of confiderable difficulty: the Author accordingly intends to profecute the fubject in a fubfequent paper.
The only Articles which relate to Medicine, are the 12th, in which Mr. S. F. Simmons communicates the cafe of a patient who voided ftones through a fiftulous ulcer in the loins, without any concomitant difcharge of urine through the fame paffages; and the 8th and 9th, which contain Dr. Prieftley's and Dr. Price's obfervations on the infalubrity of marshy fituations. Of these two papers we have already given fome
account in the foregoing review of Dr. Prieftley's experi
MATHEMATICAL PAPERS. Article 20. M. de Luc's Rule for measuring Heights by the Baro meter, reduced to the English Meajure of Length, &c. By the Aftronomer Royal.
Article 30. On the fame Subject. By Samuel Horley, LL. D.
The rule which M. De Luc deduced, from his accurate and laborious course of experiments, for calculating the heights of places by that of the barometer accompanied with the thermometer, being expreffed in French meafures, and being adapted to thermometers of very different fcales from thote that are generally used in this country; Mr. Mafkelyne, in the firft of thefe papers, undertakes to reduce this rule to English meafure, and to adapt it to a thermometer fitted with Fahrenheit's scale; and gives the rule for finding heights by the barometer, according to formula adapted to this purpose.
In the fecond of these papers, Dr. Horfley undertakes a fimilar reduction, and arrives at the fame conclufions with the Aftronomer Royal. He enters however more largely into the general fubject; giving a fuccinct explanation of M. De Luc's original formule, as well as of the principles of theory, from which his conclufions appear to originate. He inquires mi nutely how far thefe conclufions, drawn from a long feries of experiments, agree with the geometrical theory of the atmosphere, founded on the laws of gravitation. This inquiry and comparifon turn out greatly in favour of M. De Luc's accuracy in conducting his numerous and various experiments; the refults of which the Author finds to be exactly conformable to the genuine conclufions of accurate theory; though they were not fuggested by any previous fpeculations of that kind. Some ufeful tables are annexed to this paper; which contains several curious and profound inveftigations, and may be confidered as a valuable explanatory comment on M. De Luc's elaborate performance.
In the 33d and laft Article of this volume, Mr. Swinton explains a moft remarkable monogram on the reverse of a very ancient Quinarius, never before published, or explained.' The explication of this monogram, he obferves, may not improbably enable us to explain a legend on the reverfes of other ancient Roman coins, which has hitherto been deemed by fome learned men almoft, if not altogether, inexplicable.' This Quinarius, from the antique form of the letters in the exergue, is fuppofed by the Author to have been struck at the time when filver was first coined at Rome, or about five years before the commencement of the first Punic war. The remarkable monoREV. Nov. 1774. C c gram,