any fatisfactory abftract of these Papers, which must have coft the Writer a great deal of time and labour; and are every way worthy of that moft ingenious Mechanic their Author.

Art. 35. Experiments on the Tourmalin, or Afb-ftone. By Mr. Benjamin Wilson, F. R. S. In a Letter to Dr. William Heberden, F. R. S.

The more I am acquainted with Electricity,' fays Mr. Wilson, the more I admire a wonderful fimplicity which seems to prevail in Nature, at leaft in this part which ⚫ abounds with phænomena of a very curious kind; whereof • many that have paffed under my examination of late, are fo extremely nice, that I avoid venturing to relate them, because I would not willingly subject myself to the cenfure of incautious Obfervers.'It is not impoffible, however, that the cenfure this Gentleman would avoid, will fall upon him, for the publication of the Experiments before us, many of which appear fufficiently nice to puzzle incautious Ob fervers. As the defign with which they are begun and purfued, as well as the conclufions drawn from them, are, nevertheless, extremely just and philofophical, we doubt not but all those Theorifts, who are capable of applying these elegant discoveries in the minutiae of Nature, will think themfelves extremely obliged to the attention Mr. Wilfon has paid them.

.

There are also befide the Experiments on the Tourmalin,, feveral Obfervations in this Paper well worthy the perufal of the Electricians. In the first place, the Writer attempts to fettle a dispute fubfifting among thefe Gentlemen, concerning the two Electricities. Polifhed Glafs,' fays he, upon be ing rubbed properly, has been fuppofed to give an Electri'city to bodies, and thofe bodies that receive it from the glafs, are faid to be electrified plus. Whereas Wax, Amber, &c. upon being rubbed in the fame manner, have, on 'the contrary, been fuppofed to receive an Electricity from 'bodies, and those bodies which part with it are said to be ' electrified minus. But no experiment, that I know of, has yet appeared to determine which of thefe Electricities does really electrify plus, and which of them does really electrify minus; though it happens that the fact turns out just as they have all along supposed.

In a fecond treatise upon the subject of Electricity, that I published in the year 1748, feveral Experiments were produced, to fhew that all bodies are furrounded with a Me

<dium, which is of an exceeding elaflic nature, and extends but to a very finall distance from the body when it is not disturbed by heat, or other caufes. Since that, other experiments of the like kind have been published in a work, wherein my late worthy friend Dr. Hoadley was concerned with me. Among the proofs therein given, is a curious one, which I obferved in the Torricellian Vacuum, where the appearance was remarkably fenfible. And what is more fingular, that fame appearance not only proves the existence of a Medium, at or on the surface of bodies, but at the fame time deter• mines which of the Electricities is truly plus, and which of them is minus.'

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nus.

From this Experiment, which, indeed, is no less convincing than curious, it is determined that Glass, and fimilar fubitances, electrify bodies plus, and Refin, and the like, miOn the remarkable appearance, however, above hinted at, in the Torricellian Vacuum, we conceive, Mr. Wilson's reafoning not fo accurate as it might be. This appearance was that of an extraordinary light on the furface of the Mercury from which he concludes, that all bodies are furrounded by a Medium which is of an exceeding claftic nature, and extends but to a very small distance from the body.—That all bodies are furrounded by an elaftic Medium, there are experiments enough to prove: but why fhould this Medium extend but to a very small diftance from the body? If it be so very claftic, what confines it to the furface of fuch body? Will it be faid Gravity? No body can be attracted that does not itself alfo attract; and as for the Gravity of any Medium that exifts in a Torricellian Vacuum, it will hardly be infifted on. But it will be said, perhaps, if the elaftic medium extends equally throughout the distance between bodies, how came the light in the above cafe to be fo much greater on the furface of the mercury than in any other part of the Vacuum? -To this question, however, we may anfwer, for a very good reafon, because the current of the fluid was refifted by that furface and part of the light reflected. And that this is the reason is plain; becaufe, if that light were owing to any collifion between the particles of the fluid and the particles of the fuppofed atmosphere of the body, how comes it that where the fluid paffes out of the body there is not the fame phænomenon as at the furface where it paffes in? Is it not obvious that it is, because, as the Writer obferves in the one cafe, it meets with no obftacle, and, in the other, with a very great one?

Again, Mr. Wilfon controverts the opinion of Dr. Frank-. lin, concerning the impermeability of Glafs by Electricity, on which great part of the Doctor's fcheme is founded; proving from experiments, that Glafs is really permeable. Indeed the general tenour of Electrical experiments ferves to prove, that there is no natural body fo fully faturated with electrical fire as to admit no more; or fo retentive of it, as not to fubfift with lefs. The excited Electricity is alfo evidently relative; bodies being electrified apparently pius or minus, as the other bodies are with which the experiment is made.

Art. 36. New Experiments and Obfervations concerning Electricity, by Robert Symmer, Efq; F. R. S.

This article confifts of four Papers; the first relating to the Electricity of the human body, and the animal substances, filk and wool. The fecond treats of the Electricity of black and white filk; the third of the electrical cohefion, exemplified in that of two stockings electrified and in the fourth, the Writer makes an effay towards the theory of Electricity; the operations of which, he conceives, depend not upon one fingle pofitive power, according to the generally received opinion, but upon two diftinct, pofitive, and active powers, which, by contrafting, and, as it were, counteracting each other, produce the various phænomena of Electricity. The experiments Mr. Symmer here communicates to the Society, are at once fo fimple and curious, that we fhall juft mention one or two of the most remarkable.

Having obferved, as fome others have done before, that upon pulling off his ftockings at night, they frequently made a crackling or fnapping noife; and in the dark emitted sparks of fire; he proceeded to make experiments on various kinds of stockings, as thread, cotton, filk, and worsted; as alfo under different circumftances, as worn fingle, double, &c. the refult of all which experiments feemed to prove, that a combination of filk and worfted was neceffary for the production of Electricity. In this perfuafion, he proceeded with his experiments to the following very fingular one, which we fhall give in his own words.

I was at that time in mourning, fo that my filk ftockings ' were black, and under them I conftantly wore thin white worfted. About the latter end of November I went out of mourning, and of courfe changed the colour of my stockings. On the fecond of December, having put on a pair ' of white filk above the worsted, after I had wore them fome hours

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hours, I refolved to amufe myself with a few experiments. The weather was remarkably favourable, and I had reafon to expect a fine appearance of Electricity but upon taking off my ftockings, and pulling them afunder, to my great aftonifhment I found they difcovered no figns of electrical power; as i held them in my hands they hung down collapfed, and did not more attract one another, than before they were put upon my leg. I repeated the experiment two or three times, but with no better fuccefs. An event I fo little expected, difconcerted me much. I faw I was no longer to afcribe Electricity to the combination of filk and wofted; but I remained at a lofs to know to what I fhould afcribe it. At laft, upon confidering the circumstances of this and other experiments, a conjecture occurred, that the Electricity in question might depend upon the nature of dif6 ferent colours. In order to determine this, I thought it faireft to make the trial in the fame fubftances. Accordingly I had recourfe to the following experiment.

I took a pair of white filk ftockings, and having warmed them at the fire, put them both upon the fame leg. After I had worn them about ten minutes, I took them off, and pulled them afunder, but difcovered no figns of Electricity in either. I did the fame with a pair of black filk, but to no other effect. I then proceeded to the decifive trial. I put a black and a white stocking upon my leg, and wore them likewife ten minutes. I waited with fome impatience to fee the fuccefs of my experiment, and in return had the fatisfaction of obferving, upon their being pulled afunder, that each of them had acquired a ftronger degree of Electricity than I had before feen: they were inflated so much, that each of them fhewed the entire fhape of the leg, and at the diflance of a foot and a half they rushed to meet each other, I went through the fame experiment with worsted ftockings, and found that, as in filk, nothing but the combination of black and white produced Electricity. As I had often experienced the power of Electricity in the combination of black filk with white worsted stockings, there remained to try but that of white filk with black worsted, which anfwered as I expected, and feemed to compleat the demonftration.'

Mr. Symmer farther obferves, that of black and white filk ftockings, the white are always electrified pofitively, and the black negatively. He tells us alfo, that he charged a fmall phial, filled with quickfilver, with the Electricity of four

ftockings

ftockings fo ftrongly, that by the explosion he kindled fpirits of wine, and felt the blow from his elbows to his breaft.

This Gentleman's experiments alfo, regarding the cohesion of electrified stockings are new and curious; but we cannot afford more room for this article.

Art. 38. An Attempt to account for the regular diarual Variation of the horizontal Magnetic Needle, and aljs for its invigador Variation at the Time of an Aurora Borealis." By John Canton, M. A. and F. Ř. S.

The diurnal Variation of the Needle, Mr. Canton has obferved, is for the most part regular; at least out of fix hundred and three days obfervations, he found it was fo in five hundred and seventy-four of them. That is, he found the abfolute Variation of the Needle wef ward, increafed from about eight or nine o'clock in the morning, till about one or two in the afternoon, when the Needle became ftationary for fome time; after which that Variation decreafed, and the Needle came back again to its former fituation, in the tight, or by the next morning. The diurnal Variation is irregular, when the Needle moves flowly eastward in the latter part of the morning, or weftward in the latter part of the afternoon; also when it moves much either way in the night, or fuldenly both ways in a fhort time. Thefe irregularities happen feldom, and are always accompanied with an Aurora Borealis. To account for thefe Variations, Mr. Canton (beginning with the regular) remarks, that the attractive power of the Magnet decreafes while the Magnet is heating, and increases while it is cooling. This he proves alfo by experiment; after which he gives the following reafon for this phænomenon.

It is evident, that the magnetic parts of the earth in the north on the caft fide, and the magnetic parts of the earth in the north on the weft fide of the magnetic meridian, equally attract the north end of the Needle. If then the ⚫eaftern magnetic parts are heated fafter by the fun in the morning than the weftern, the Needle will move weftward, and the abfolute Variation will increafe; when the attracting parts of the earth on each fide the magnetic meridian. have their heat increafing equally, the Needle will be ftationary, and the abfolute Variation will then be greateft; but, when the western magnetic parts are either heating fafter, or cooling flower, than the eastern, the Needle will move eastward, or the abfolute Variation will decrease; and when the eaftern and western magnetic parts are coolH 4 • ing