of Lord Bacon's MAGNALIA NATURÆ, which, as he obferves, fere Extra VIAS TRITAS, et ORBITAS NOTAS, jacent, and in the difcovery of which, he adds, Etiam ABSURDITAS rei aliquando juvet. To leffen however any feeming abfurdity, in the prefent inftance, we need only to remind our readers of Mr. Hunter's obfervation (which we gave in our Journal for September laft, p. 223,) of the very liberal diftribution of nerves to the electric organs of the torpedo:-a circumftance which feems ftrongly to mark a relation between the electric fluid and the nerves, the undoubted inftruments of mufcular motion. Not many years ago it appeared to us, and poffibly to others, as improbable that the phenomena of the torpedo fhould be caufed by the electric matter, as it may now appear that the fponta neous motions of men and other animals fhould be the effects of the fame agent. To recur to the infancy of electricity,What fober, or even bold philofopher, who faw amber attract ftraws, in the days of Thales and Theophraftus, could fufpect that the agent in this trifling appearance, was the cause of thunder, and poffibly of earthquakes?

We shall close our account of this work with a curious obfervation, relating to a fingular property of the electric fluid; concerning which we have lately difcovered fo much, and yet perhaps know fo little. The nearest approaches that had hitherto been made to a Vacuum feemed to prove that it was a conductor of the electric matter; which was found to ftrike at a greater diftance, or to be tranfmitted through a greater space, in proportion as the air had been more carefully exbaufted. Mr. Walth, however, having been affifted by M. de Luc in making a more perfect vacuum in the arched barometer, by boiling the quickfilver in the tube, found that the electric fpark or fhock would no more pafs through this empty space, than through a flick of felid glass. Some fubfiance, therefore, the Author infers, is probably neceffary to conduct electricity; which he fuppofes to be incapable, by its own expanfive power, of extending itfelf into spaces void of all matter, as hath gene. rally been fuppofed, on the idea of there being nothing to obstruct its paffage.'

ART. VIII. PHILOSOPHICAL TRANSACTIONS, Vol. LXIV. 4to. 7 s. 6 d. fewed. Davis. 1774.

Part 1.

PAPERS relating to ASTRONOMY.

Article 1. Obfervations on the Solar Spots. By Alexander Wilfon, M. D. Profeffor of Practical Aftronomy in the Univer fity of Glafgow, &c.

HE opinions that have been formed concerning the nature, origin, and fituation of the folar, fpots have been various; as might be expected on a fubject so very remote from

THE

human

human investigation. The ingenious Author of this paper, by attending particularly to the different phases presented by the umbra, or fhady zone, of a spot of an extraordinary fize that appeared upon the fun, in the month of November 1769, during its progrefs over the folar difc, was led to form a new and fingular conjecture concerning the nature of these appearances; the juftice of which was afterwards confirmed by repeated observations.

The refults of these obfervations are-that the folar macule are cavities in the body of the fun; that the nucleus (as the middle or dark part has been usually called) is the bottom of the excavation; and the umbra, or fhady zone ufually furrounding it, is the shelving fides of the cavity. The Author appears not only to have very fatisfactorily afcertained the reality of these immenfe excavations in the fun's body, but has pointed out a method of measuring the depth of them. He estimates, in particular, that the nucleus, or bottom of the large spot abovementioned, was not lefs than a femidiameter of the earth (or about 4000 miles) below the level of the fun's furface; while its other dimenfions were of a much larger extent.

He obferved that when a spot, in the middle of the fun's difc, where it is furrounded equally on all fides with its umbra, comes near the western limb of the fun; that part of the umbra which is next to the fun's center gradually diminishes in breadth, and at length, when the spot reaches within about a minute of the limb, totally disappears; while the umbra, on the other fide of it, continues nearly of its former dimenfions. If, after the period of half a revolution, the fpot appears again, on the oppofite fide of the difc; that part of the umbra, which had before disappeared, and which is now on the left hand side of the nucleus, is now plainly to be feen: but the umbra on the other fide of the fpot, or that which is next to the fun's center, seems to have vanished in its turn; being hid from the view by the upper edge of the excavation, or by the oblique pofition of its floping fides with refpect to the eye. As the fpot however advances on the fun's furface, this umbra, or fide of the cavity, comes in fight; at first appearing narrow, but afterwards gradually increafing in breadth, in proportion as the spot moves toward the middle of the difc.

Thefe appearances, in particular the gradual diminution and difappearance, as well as the re-appearance and gradual enlargement, of the umbra, on the one fide or other of a spot, according as it advances near the weftern limb, or proceeds onwards from the eastern edge of the fun, are naturally accounted for by the Author's fuppofition, that the umbra are inc floping fides of a cavity, which will appear under different angles or of dif

ferent

ferent breadths, or totally disappear, according to their pofition with refpect to the eye of the fpectator. Thefe appearances, at least, perfectly refemble the phafes that would be exhibited by an excavation in a spherical body, made to revolve on its axis'; the bottom of the cavity being painted black, and the fides lightly fhaded.

It feems evidently to follow from thefe and the Author's other obfervations, that the body of the fun, at the depth of the nucleus, either emits no light, or emits fo little as to appear dark when feen at the fame time, and compared, with that refplendent, and probably, in fome degree, fluid fubftance that covers his furface. This manner of confidering thefe phenomena naturally gives rife to many curious fpeculations and inquiries. It is natural, for inftance, to inquire by what great commotion this refulgent matter is thrown up on all fides, fo as to expose to our view the darker part of the fun's body, which was before covered by it?-what is the nature of this fhining matter?-and why, when an excavation is formed in it, is the luftre of this fhining fubftance, which forms the shelving fides of the cavity, fo far diminished, as to give the whole the appearance of a fhady zone, or darkish atmosphere, furrounding the denuded part of the fun's body? On these and many other fubjects of inquiry, the Author advances fome ingenious conjectures; for which we muft refer the curious to the perusal of the article at large.

Article 11. An Improvement propofed in the crofs Wires of Telefcopes: By the fame.

The Author of the preceding Article propofes in this Paper a method, which he has fuccefsfully employed, of diminishing confiderably the vifible fubtenfe of the angle formed by the thickness of the cross wires ufed in telescopes, which workmen have not yet been able to draw fine enough for that purpofe. The means by which he has effected this diminution are exceedingly fimple, as they confift in nothing more than flattening the fmalleft wires that are now drawn, and then fixing thefe Battened wires in the telescope, with the edge towards the eye. Several lengths of fine filver wire, marked 500 to the inch, are fixed, at each extremity, on the fmooth, flat furface of a small block of steel. A fimilar fteel block is laid over them, which, on giving it a fmart ftroke with a hammer of about five pounds weight, flattens all the wires in a very even 'manner. The diminution thus produced is faid to be more confiderable than could be obtained by manufacturing finer wires; unless they could be drawn to the fmall fize of 2 or 3000 to the inch.

Article

Article 13. The Disparition of Saturn's Ring, obferved by Jofeph Varelez, Lieutenant of the Royal Navy of the King of Spain, &c.

To explain the title and fubject of this Article, we shall premife that when Saturn is in fuch a fituation, as that the plane of his ring paffes through the fun, or through the eye of an obferver on the earth, his ring wholly difappears; either, because in the first place, neither of the flat furfaces of the ring receives any light from the fun, nor can confequently reflect any to us; or, in the latter, because the edge of the ring, which is now directed to the earth, is fo thin, as not to be capable of reflecting back to us a quantity of the fun's light fufficient to render it vifible. In either of thefe pofitions, which are not very different from each other, Saturn will appear round, like any of the other planets *.

In this Article a fhort account is given of the observations made by the Author, on the difappearance of the ring in October laft. After having feen both the anfe diftinctly, through a good telescope, from the 24th of September to the 4th of October, he obferves that, on the 5th, he could only perceive the western anfa. On the 6th, the atmosphere being thick, he fancied he could ftill difcern fome faint remains of the ring: but on the 7th, the fky being clearer than he had ever yet feen it, no part of the ring was vifible; fo that he is convinced ⚫ that this famous phenomenon took place on the 6th day of the month. The moft ftriking circumftances of this phenomenon,' the Author immediately adds, were the following:'

1. The occidental anfa conftantly appeared more bright than the oriental. 2. On the difc of the planet, one could clearly distinguish the line of the fhadow projected from the thickness of the ring. 3. On the extremities of this, fome luminous points were perceived, which reflected the light more ftrongly than the others. 4. I did not obferve a fenfible variation in the apparent diameter of the ring.'

"

There is an ambiguity in the preceding paffage which we cannot clear up without fuppofing that by the circumftances of this phenomenon,' the Author muft mean, the circumstances that preceded or followed the difappearance of the ring; as the anfæ, or points, more or lefs luminous, could not be perceived in an invifible ring,

It will be fufficient barely to mention the subjects treated in the remaining aftronomical Articles. Articles 2 and 3 contain

M. Maraldi has given a very clear and circumftantial account of this celebrated phenomenon, its periods and phafes, &c. in the Memoirs of the Academy of Sciences at Paris for the years 1715 and 1716.

obfervations

obfervations made by the miffionaries at Pekin. In Numbers 21, 22, 23, 24, and 25, are likewife contained various aftronomical obfervations, particularly of immersions and emersions of Jupiter's fatellites, made by Samuel Holland, Esq; Enfign George Sproule, Mr. Thomas Wright, and others, employed by government in furveying different parts of North America; together with calculations of the longitudes of various places, deduced from thefe obfervations, by the Aftronomer Royal, Some short remarks on the folar fpots, by Mr. Humphry Marfhall, Pennfylvania, form the fubject of the 26th Article.

PAPERS relating to ELECTRICITY and METEORS. Article 7. Electrical Experiments by Mr. Edward Nairne of London, Mathematical-Inftrument-Maker, made with a Machine of his own Workmanship, &c.

This machine, a defcription of which is annexed, illuftrated with a plate, appears to poflefs powers greater than those of any electrical apparatus we have yet met with. It confifts of a glass cylinder 19 inches long, and 12 inches in diameter, which is rubbed by a cushion 14 inches long and 5 inches broad. The conductor is 5 feet long, and a foot in diameter. At the farther extremity of it is inferted a fhort brass rod terminating in a ball. The fparks which proceed from this ball, on exciting the cylinder, are of a furprizing length. I have frequently,' fays the ingenious Conftructor of this machine, drawn electrical fparks at the diftance of 12, 13, or 13 inches from the prime conductor. These were indeed the diftances, to which the electrical fire would commonly ftrike. It would fometimes reach the distance of fourteen inches; but this was but feldom.'

6

Several curious experiments and practical obfervations are fubjoined to the Author's defcription of his machine, for which we must refer to the article itself. We fhall only relate, in a fummary manner, the fubftance of one of these experiments, the result of which feems fully to juftify the preference which the majority of electricians, we believe, ftill continue to give to pointed terminations of the conductors erected for the prefervation of buildings and fhips; notwithstanding the objections that have been made to that mode of construction, through an apprehenfion that the electric matter is invited to strike conductors thus terminated.

A fmall infulated conductor, having a ball at each end, was placed fo as that one of thefe balls might receive fparks proceeding from the large conductor abovementioned, at the dif tance of four inches. Under the ball at the other extremity was placed a little apparatus, communicating with the earth, which would occafionally receive either a fharp pointed wire, or another wire terminating in a ball or knob. On fixing the pointed wire at the diftance of three or four inches below the

laft