its channel down to "the furface of the rock, and between fix and feven feet wide, but in times of floods extended itself entirely over the valley.

Researches have been made for the gold, amidst the fand and gravel along the run of the brook, for near half a mile in length; but it is only about one hundred and fifty yards above, and about two hundred yards below the ford, that the trials have been attended with much fuccess: within that space, the valley is tolerably level, and the banks of the brook have not more than five feet of fand and gravel above the rock; added to this, it takes a small turn to the fouth, ward, and, confequently, the rude furfaces of the shiftus rock in fome degree cross its course, and form natural impediments to the particles of gold being carried further down the stream, which ftill lower has a more rapid defcent; befides, the rude manner in which the country people worked, feldom enabled them to penetrate to the rock, in those places where the fand and gravel were of any material depth. Their method was, to turn the course of the water wherever they deemed neceffary, and then, with any infiruments they could procure, to dig holes down to the rock, and by wathing, in bowls and fieves, the fand and gravel they threw out, to feparate the partiles of gold which it contained; and from the slovenly and hatty way in which their operations were performed, much gold most probably efcaped their search; and that indeed actually appears to have been the cafe, for fince the late rains washed the clay and gravel which had been thrown up,

gold has been found lying on the furface. The fituation of the place, and the conftant command of water, do, however, very clearly point out the great facility with which the gold might be separated from the trath, by adopting the mode of working practifed at the best managed tin stream works in the county of Cornwall; that is, entirely to remove (by machinery) the whole cover off the rock, and then wath it in proper buddies and fieves. And by thus continuing the operations, constantly advancing in the ravine towards the mountain, as long as gold should be found, the vein that forms its matrix might probably be laid bare.

The discovery was made public, and the workings began, early in the month of September laft, and continued till the 15th of October, when a party of the Kildare militia arrived, and took poffeffion by order of government; and the great concourse of people, who were bufily engaged in endeavouring to procure a thare of the treafure, immediately defitted from their labour, and peaceably retired. Calculations have been made, that during the foregoing period, gold to the amount of three thoufand pounds Irish sterling was told to various persons; the average price was three pounds fifteen thillings per ounce; hence eight hundred ounces appear to have been collected within the short space of fix weeks.

The gold is of a bright yellow colour, perfectly malleable; the fpecific gravity of an apparently clean piece 19,000. A fpecimen, affayed here by Mr. Weaver, in the moift way, produced from 24 grains, grains, 22 grains of pure gold, and 14 of filver. Some of the gold is intimately blended with, and adherent to quartz; fome (it is faid) was found united to the fine grained iron ftone, but the major part was entirely free from the matrix: every piece more or lefs rounded on the edges, of various weights, forms, and fizes, from the most minute particles up to 2 oz. 17 dwt.; only two pieces are known to have been found of superior weight, and one of those is 5, and the other 22 ounces. (

Í much regret not having been present when the work was going on, that I might have seen the gold as found, before prepared for fale by breaking off any extraneous matter thatadhered; for in that ftate, a proper attention to the substances with which it was united, and a fubiequent diligent inspection of the several veins that range through the mountain, might assist towards the discovery of that from whence it was detached.

I shall shortly return to England; and on my arrival, will fend specimens of the gold, and of the different substances of the mountain, 'to be depofited (if you think proper) in the collection of the royal society.

And am, with great refpcct, &c. ABRAHAM MILLS.

The bearings are all taken by the compass, without allowing for the variation.

BESIDES these accounts of the gold found in Ireland, the following information has been received on that fubject.

William Molesworth, Eiq. of Dublin, in a letter to Richard

Molefworth, Efq. F. R. S. writes, that he weighed the largest piece of gold in his balance, both in air and water; that its weight was 20 Oz. 2 dwt. 21 gr. and its specific gravity, to that of sterling gold, as 12 to 18. Alfo that Richard Kirwan, Esq. F R. S. found the specific gravity of another spcimen to be as 13 to 18. Hence, as the gold was worth £ 4 an ounce, Mr. William Molefworth concludes that the specimens are full of pores and cavities, which increase their bulk, and that there are some extraneous fubfiances, fuch as dirt or clay, contained in those cavities.

This opinion was discovered to be well founded, by cutting through fome of the small lumps.

STANESBY ALCHORNE, Esq. his maiefty's aflay-mafter at the Tower' of London, affayed two specimens of this native gold. The first appeared to contain, in 24 carats, 21 of fine gold;

On the Cold felt on bigh Mountains, and at great depths, from Dr. Hunter's translation of buler's Letters 10 a German Princess.

IT appears ver y furprizing, that we should feel the same degree of cold in all regions, after we have risen to a certain height, say 24,000 feet; confidering that the variations with respect to heat, on the earth, not only in the different climates, but in the fame country, at different seasons of the year, are so perceptible. This variety, which takes place at the furface of the globe, is undoubtedly occafioned by the fun. It appears, at first fight, that his influence must be the fame above and below, especially when we reflect, that a height of 24,000 feet, or a mile, though very great with refpect to us, and even far beyond the height of the loftieft mountains, is a mere nothing, com. pared to the distance of the fun. which is about thirty millions of miles*. This is therefore, a very important difficulty, which we muft endeavour to folve. For this purpose I begin with remarking, that the rays of the fun do not communicate heat to any bodies, but such as do not grant them a free paflage. You know that bodies, through which we can difcern objects, are denominated tranfparent, pellucid, and diaphonous. These bodies are glass, crystal, diamond, water, and several other liquids, though fome are more or lefs tranfparent than others. One of these transparent bodies being exposed to the fun, is not heated to fuch a degree as a body not tranfparent, as wood, iron, &c. Bodies not transparent are denominated opaque. A burning-glass, for example, by tranfmitting the rays of the fun, fets on fire opaque bodies, while the glass itself is not fenfibly heated. Water exposed to the fun

becomes fomewhat warm, only because it is not perfectly transparent; when we fee it confiderably heated by the fun at the brink of rivers, it is because the bottom, being an opaque body, is heated by the rays which the water tranfmits. Now, every heated body communicates that heat to all adjoining bodies; the water accordingly derives heat from the bottom. If the water be very deep, fo that the rays cannot penetrate to the hottom, it has no preceptible heat, though the fun bears upon it.

As air is a very transparent body, to a much higher degree than glass or water, it follows, that it cannot be heated by the fun, because the rays are freely tranfmitted through it. The heat which we frequently feel in the air, is communicated to it by opaque bodies, which the rays of the fun have heated; and were it poffible to annihilate all these bodies, the air would scarcely undergo any change in its temperature by the rays of the fun: exposed to it or not, it would be equally cold. But the atmosphere is not perfectly transparent: it is even fometimes so loaded with vapours, that it loses almost entirely its transparency, and presents only a thick fog. When the air is in this state, the rays of the fun have a more powerful influence upon it, and heat it immediately.

But these vapours rise to no great height; at the height of 24,000 feet, and beyond, the air is fo fubtile and fo pure, that it is perfectly transparent; and for this reason the rays of the iun cannot immediately produce any effect upon it. This air is likewise too

remote from terreftrial bodies, to receive a communication of heat from them; they act only upon fuch as are adjacent. Hence you will eafily perceive, that the rays of the fun cannot produce any effect in regions of the air very much elevated above the furface of the earth; and that the fame degree of cold must always, and universally, prevail in such regions, as the fun has no influence there, and as the heat of terreftrial bodies cannot be communicated fo far. This is nearly the cafe on the summit of very high mountains, where it is always much colder than on plains and in vallies *.

The city of Quito, in Peru, is almost under the equator, and were we to form our judgment from its fituation on the globe, we would suppose it opprefled with intolerable heat; the air, however, is abundantly temperate, and differs very little from that of Paris. Quito is situated at a great height above the real furface of the earth. In going to it from the fea thore, you have to afcend for feveral days; it is accordingly built in an elevation equal to that of our highest mountains, though furrounded by others still much higher, called the Cordeliers. This laft circumftance would afford a reason for thinking,

that the air there must be as hot as at the furface of the earth, as it is contiguous, on all fides, to opaque bodies, on which the rays of the fun fall. The objection is folid; and no folution can be given but this. That the air at Quito, being very elevated, must be much more fubtile, and of less gravity than with us, and the barometer, which always ftands confiderably lower, inconteftably proves it.

Air of fuch a quality is not fo fufceptible of heat as common air, as it must contain less vapour and other particles which usually float in the atmosphere; and we know by experience, that air, very much loaded, is proportionably fufceptible of heat. I must here fubjoin another phenomenon, no lets furprizing: In very deep pits, and lower fstill, if it were still possible to defcend, the fame degree of heat always, and univerfally, prevails, and nearly for the fame reafon. As the rays of the fun exert their influence only on the furface of the earth, and as the heat which they there excite communicates itfelf up and down, this effect, at very great depths, is almost imperceptible. The fame thing holds respecting confiderable heights. This elucidation will, I flatter myfelf, prove fatisfactoryt.

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