be difcerned in them. These three fpots are plainly to be diftinguifhed from the rest of the marks upon the moon; for the reflection of the fun's rays from the earth is, in its prefent fituation, fufficiently bright with a ten-feet reflector, to fhew the moon's spots, even the darkest of them: nor did I perceive any fimilar phenomena laft lunation, though I then viewed the fame places with the fame inftrument.

"The appearance of what I have called the actual fire or eruption of a volcano, exactly refembled a fmall piece of burning charcoal, when it is covered by a very thin coat of white afhes, which frequently adhere to it when it has been fome time ignited; and it had a degree of brightnefs, about as trong as that with which fuch a coal would be feen to glow in faint daylight.

All the adjacent parts of the volcanic mountain feemed to be faintly illuminated by the eruption, and were gradually more obfcure as they lay at a greater distance from the crater.

"This eruption refembled much that which I faw on the 4th of May, in the year 1783; an account of which, with many remarkable particulars relating to volcanic mountains in the moon, I fhall take an early opportunity of communicating to this fociety. It dif

fered, however, confiderably in magnitude and brightnefs; for the volcano of the year 1783, though much brighter than that which is now burning, was not nearly fo large in the dimenfions of its eruption: the former feen in the telescope refembled a star of the fourth magnitude as it appears to the natural eye; this, on the contrary, fhews a vifible difk of luminous matter, very different from the fparkling brightness of starlight.

P. S. M. Méchain having favoured me with an account of the difcovery of his comet, I looked for it among the Pleiades, fuppofing its track fince the 10th of this month to lie that way; and faw it April 19th, at 10 h. 10' fidereal time, when it preceded FL ả Pleiadum about 54′′ in time, with nearly the fame declination as that ftar; but no great accuracy was attempted in the determination of its place. As I have mentioned the comet in a foregoing paragraph of this paper, I thought it proper here to add my obfervation of it. "The comet is nearly round, with

a fmall tail towards the north "following part; the chevelure "extends to about four or five "minutes; and it has a central, "very fmall, ill-defined nucleus, "of no great brightnefs."

THOMPSON, Knt. F. R.S.

By Sir BENJAMIN

in order to fee if I could difcover any relation between the conducting powers of thofe fubftances, and their power of abforbing moisture from the atmosphere, I made the following experiments.

"Having provided a quantity of each of the undermentioned fubftances, in a state of the most perfect cleanness and purity, I expofed them, fpread out upon clean Chinaplates, twenty-four hours in the dry air of a very warm room (which had been heated every day for feveral months by a German stove), the last fix hours the heat being kept up to 85° of Fahrenheit's thermometer; after which I entered the room with a very accurate balance, and weighed equal quantities of thefe various fubftances, as expreffed in the following table.

"This being done, and each fubftance being equally fpread out upon a very clean China plate, they were removed into a very large uninhabited room upon the fecond floor, where they were expofed 48

The various fubftances.

hours, upon a table placed in the middle of a room, the air of the room being at the temperature of 45° F.; atter which they were carefully weighed (in the room) and were found to weigh as under men. tioned.

"They were then removed into a very damp cellar, and placed upon a table, in the middle of a vault, where the air, which appeared by the hygrometer to be completely faturated with moisture, was at the temperature of 45° F.; and in this fituation they were fuffered to remain three days and three nights, the vault being hung round, during all this time, with wet linen cloths, to render the air as damp as poffible, and the door of the vault being

fhut.

"At the end of the three days I entered the vault, with the balance, and weighed the various fubftances upon the fpot, when they were found to weigh as is expreffed in the third column of the following table.

Seep's wool

Silk {Ravelings of white taffety

1057

1107

Linen {Ravelings of fine linen

lint

1046

1102

Cotton wool

gold lace.

N. B.

N. B. The weight made ufe of in thefe experiments was that of Cologne, the parts or leaft divifions being part of a mark, confequently oco of thefe parts make about 52 grains of Troy.

"I did not add the filver wire to the bodies above mentioned from any idea that that fubfiance could poffibly imbibe moisture from the atmosphere; but I was willing to fee whether a metal, placed in air faturated with water, is not capable of receiving a fmall addition of weight from the moisture attracted by it, and attached to its furface; from the refult of the experiment, however, it fhould feem that no fuch attraction fubfifts between the metal I made ufe of, and the watery vapour diffolved in air.

I was totally miftaken in my conjectures relative to the refults of the experiments with the other fubftances. As linen is known to at tract water with fo much avidity; and as, on the contrary, wool, hair, feathers, and other like animal fubstances, are made wet with fo much difficulty, I had little doubt but that linen would be found to attract miure from the atmosphere with much greater force than any of thofe fubftances; and that, under fimilar circumftances, it would be found to contain much more water: and I was much confirmed in this opinion upon recollecting the great difference in the apparent dampnefs of linen and of woollen clothes, when they are both expofed to the fame atmosphere. But thefe experiments have convinced me, that all my fpeculations were founded upon erroneous principles.

"It fhould feem, that thofe bodies which are the most eafily wet, or which receive water, in its unelaftic form with the greatest case, are not thofe which in all cafes at

tract the watery vapour diffolved is the air with the greatest force.

"Perhaps the apparent dampness of linen, to the touch, arifes more from the ease with which that fubftance partswith the water it contain, than from the quantity of water it actually holds: in, the fame manner as a body appears hot to the touch, in confequence of its parting freely with its heat, while ano her body, which is actually at the fame temperature, but which witholds its heat with greater obstinacy, affects the fenfe of feeling much lefs violently.

"It is well known, that woollen clothes, fuch as flannels, &c. worn next the fkin, greatly promote infenfible perfpiration. May not this arife principally from the ftrong attraction which fubfits between wool and the watery vapour which is continually iffuing from the human body?

"That it does not depend entirely upon the warmth of that covering, is clear; for the fame degree of warmth, produced by wearing more clothing of a different kind, does not produce the fame effect.

"The perfpiration of the human body being abforbed by a covering of flannel, it is immediately ditiributed through the whole thickness of that fubftance, and by that means expofed by a very large furface to be carried off by the atmosphere; and the lofs of this watery vapour, which the flannel fuftains on the one fide, by evaporation, being immediately restored from the other, in confequence of the frong attraction between the flannel and this vapour, the pores of the fkin are difencumbered, and they are continually furrounded by a dry, warm, and falubrious atmosphere.

"I am aftonifhed, that the cuftom of wearing flannel next the fkin

fhould

fhould not have prevailed more uni. Verfally. I am confident it would prevent a multitude of difeafes; and I know of no greater luxury than the comfortable fenfation which arifes from wearing it, efpecially after one is a little accustomed

to it.

"It is a mistaken notion, that it is too warm a cloathing for fummer. I have worn it in the hottest climates, and in all feafons of the year, and never found the leaft inconvenience from it. It is the warm bath of a perfpiration confined by a linen flirt, wet with fweat, which renders the fummer heats of fouthern climates fo infupportable; but flannel promotes perfpiration, and favours its evaporation; and evaporation, as is well known, produces politive cold.

"I firit began to wear flannel, not from any knowledge which I had of its properties, but merely upon the recommendation of a very able phyfician (fir Richard Jebb); and when I began the experiments of which I have here given an account, I little thought of difcovering the phyfical caufe of the good effects which I had experienced from it; nor had I the most distant idea of mentioning the circumftance. I fhall be happy, however, if what

1

I have faid, or done, upon the fubject, fhould induce others to make a trial of what I have fo long experienced with the greater advantage, and which, I am confident, they will find to contribute greatly to health, and confequently to all the other comforts and enjoyments of life.

"I fhall then think thefe expe. riments, trifling as they may appear, by far the mott fortunate, and the niot important ones I have ever made.

With regard to the original object of thefe experiments, the difcovery of the relation which I thought might poffibly fubfift between the warmth of the fubftances in quellion, when made ufè of as cloathing, and their powers of attracting moisture from the atmofphere; or, in other words, between the quantities of water they contain, and their conducting pow ers with regard to heat; I could not find that thefe properties depended in any manner upon, or were in any way connected with, each other."

"The refult of my experiments upon the conducting powers of thefe fubitances, I referve for a future communication."

plains of Hindoftan, and is distant from Lucknow about two hundred miles N. E. The town is a principal mart, where the commodities of the mountains are exchanged for thofe of the plain. The raja, or prince of the country, holds his poffeffions in the hills as an independent fovereign; but for thofe on the plain he owes fealty, and pays tribute to the vizier. He therefore embraced this opportunity paying homage in perfon to his lord. During his itay at court, I had an opportunity of making the enquiries I wished from his people, and particularly from his dewan or minifter, who had with him fome of the inhabitants of the place where the borax is made.

"This faline fubftance, called in the language of this country fwa gab, is brought into Hindoftan from the mountains of Tibbet. The place where it is produced is in the kingdom of Jumlate, diftant from Betowle about thirty days journey north. Jumlate is the largest of the kingdoms in that part of the Tibbet mountains, and is confidered as holding a fuperiority over all the reft.

"The place where the borax is produced is defcribed to be in a fmall valley, furrounded with fnowy mountains, in which is a lake, about fix miles in circumference, the water of which is constantly hot, fo much fo that the hand cannot be held in it for any time. The ground. round the banks of the lake is perfectly barren, not producing even a blade of grafs; and the earth is full of a faline matter in fuch plenty that, after falls of rain or fnow, it concretes in white flakes upon the furface, like the natron in Hindof

tan.

Upon the banks of this lake, in the winter feafon, when the falls of how begin, the earth is tormed

into fmall refervoirs, by raifing it into banks about fix inches high; when these are filled with fnow, the hot water from the lake is thrown upon it, which, together with the water from the melted fnow, remains in the refervoir, to be partly abforbed by the earth, and partly evaporated by the fun; atter which there remains at the bottom a cake of fometimes half an inch thick, of crude borax, which is taken up and referved for ufe. It can only be made in the winter feafon, becaufe the falls of fnow are indifpenfably requilite, and also because the faline appearances upon the earth are strongest at that feafon. When once it has been made upon any fpot, in the manner above defer.bed, it cannot be made again upon the fame place, till the inow fall have fallen upon it and diffolved three or four times; after which the faine efflorefcence reappears, and it is again fit for the operation.

"The borax in the state above defcribed, is tranfported from hill to hill upon goats, and paffes through many different hands before it reaches the plains, which increases the difliculty of obtaining authentic information regarding the original manufacture. When brought down from the bills, it is refined from the earth and grofs impurities by boil ing and cryftallifation. I could obrain no anfwers to any queftion regarding the quality of the water, and the mineral productions of the foil. All they could fay of the former was, that it was very hot, very foul, and as it were greasy; that it boils up in many places, and has a very offenfive fmell: and the latter remarkable only for the faline appearances above described. That country, however, in general, pro duces confiderable quantities of iron,