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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.,

Refearches 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 fuccefs: 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 fmall turn to the fouthward, and, confequently, the rude furfaces of the thiftus rock in fome degree cross its courfe, and form natural impediments to the particles of gold being carried further down the ftream, which ftill lower has a more rapid descent; befides, the rude manner in which the country people worked, feldom enabled them to penetrate to the rock, in thofe places where the fand and gravel were of any material depth. Their method was, to turn the courfe of the water wherever they deemed neceffary, and then, with any inftruments 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 particles of gold which it contained; and from the flovenly and hafty way in which their operations were performed, much gold moft probably efcaped their fearch; and that indeed actually appears to have been the cafe, for fince the late rains wathed 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 feparated from the trath, by adopting the mode of working practifed at the beft managed tin ftream works in the county of Cornwall; that is, entirely to remove (by machinery) the whole cover off the rock, and then wash it in proper buddles and fieves. And by thus continuing the operations, confiantly advancing in the ravine towards the mountain, as long as gold fhould be found, the vein that forms its matrix might probably be laid bare.

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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 concourfe of people, who were bufily engaged in endeavouring to procure a fhare 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 fterling was fold to various perfons; the average price was three pounds fifteen fhillings 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 specific gravity of an apparently clean piece 19,000. A fpecimen,, atlayed here by Mr. Weaver, in the moift way, produced from 24

grains,

43

58

grains, 22 grains of pure gold, and 13 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 fuperior weight, and one of thofe is 5, and the other 22 ounces.

Í much regret not having been prefent 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, that adhered; for in that ftate, a proper attention to the fubftances with which it was united, and a fubfequent diligent infpection of the feveral veins that range through the mountain, might aflift towards the discovery of that from whence it was detached.

I fhall fhortly return to England; and on my arrival, will send fpecimens of the gold, and of the different fubftances of the mountain, to be deposited (if you think proper) in the collection of the royal fociety.

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

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

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

William Molefworth, Efq. 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 fpecific gravity, to that of fterling gold, as 12 to 18. Alfo that Richard Kirwan, Efq. F R. S. found the fpecific gravity of another fpcimen to be as 13 to 18. Hence, as the gold was worth £ 4 an ounce, Mr. William Molefworth concludes that the fpecimens are full of pores and cavities, which increase their bulk, and that there are fome extraneous fubftances, fuch as dirt or clay, contained in thofe ca-' vities.

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

STANESBY ALCHORNE, Efq. his majefty's affay-mafter at the Tower of London, affayed two fpecimens of this native gold. The first appeared to contain, in 24 carats, 219 of fine gold;

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we fhould feel the fame degree of cold in all regions, after we have rifen to a certain height, fay 24,000 feet; confidering that the variation's with respect to heat, on the earth, not only in the different climates, but in the fame country, at different feafons of the year, are fo 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 aboye and below, efpecially when we reflect, that a height of 24,000 feet, or a mile, though very great with respect to us, and even far beyond the height of the loftieft mountains, is a mere nothing, com. pared to the diftance 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-fuch as do not grant them a free paffage. You know that bodies, through which we can difcern objects, are denominated tranfparent, pellucid, and diaphonous. Thefe bodies are glafs, cryftal, diamond, water, and feveral other liquids, though fome are more or lefs tranfparent than others. One of these transparent bodies being expofed 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-glafs, for example, by tranfmitting the rays of the fun, fets on fire opaque bodies, while the glafs itfelf is not fenfibly heated. Water expofed to the fun

becomes fomewhat warm, only be caufe 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 commu-nicates 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 bottom, 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 fcarcely undergo any change in its temperature by the rays of the fun : expofed to it or not, it would be equally cold. But the atmosphere is not perfectly tranfparent: it is even, fometimes fo loaded with vapours, that it lofes almost entirely its transparency, and prefents 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 thefe vapours rife 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 ́ reafon the rays of the fun cannot immediately produce any effect upon it. This air is likewife too

remote

Mr. Euler always means German miles, of 4000 fathoms each, or fomewhat Ander 44 miles Englih.-E. £.

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 univerfally, prevail in fuch 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 fummit of very high mountains, where it is always much colder than on plains and in vallies

The city of Quito, in Peru, is almoft under the equator, and were we to form our judgment from its fituation on the globe, we would suppose it oppreffed with intolerable heat; the air, however, is abundantly temperate, and differs very little from that of Paris. Quito is fituated at a great height above the real furface of the earth. In going to it from the fea fhore, 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 ftill much higher, called the Cordeliers. This laft circumftance would afford a reafon 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, be ing very elevated, must be much more fubtile, and of lefs 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 lefs 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 muft here fubjoin another phenomenon, no lefs furprizing: In very deep pits, and lower ftill, if it were fill poffible 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 almoft imperceptible. The fame thing holds refpecting confiderable heights. This elucidation will, I flatter myfelf, prove fatisfactory.

Account

There are clouds, however, above thefe mountains, and in almoft as great a quantity as above the plains, which is demonftrated by the fhows which cover the higheft fummits. There are few naturalifts who have not been furprized by clouds in their excurfions upon the mountains. The heat that is felt when fuch clouds are formed, muft be attributed almost entirely to the tranfmiflion of the water which found itfelf diffolved in the air, under the form of elattic fluid, to a liquid Rate. The heat of the folar rays, intercepted by the cloud, can produce no change in the inferior temperature, as it would have been tranfmitted from the ground.-F. E.

The reafon which profeffor Euler affigns for the cold that prevails in the higher regions of the atmosphere feems plaufible, but will not ftand an accinate xamination. Light is much impaired in its paffage through the atmoiphere,

Cc4

and

Account of the Great Speckled Diver or Loon. From White's Naturalifts Calendar.

AS one of my neighbours was traverfing Wolmer foreft from Bramfhot across the moors, he found

and the heat communicated is in every cafe proportional to the quantity of abforption. It appears, from fome ingenious experiments of M. Bouguer, that we receive only four-fifths of the rays of a vertical fun; and when that luminary ap proaches the horizon, the portion of this light, which reaches the furface of the earth, is much smaller. Thus, at an elevation of 20 degrees, it is one-half; at that of 10 degrees, one-third; and at that of five degrees, one-eighth. Hence, the fun-beams are moft powerful on the fummits of lofty mountains, for they fuffer the greateft diminution in paffing through the denfe air of the lower regions. If the air derived its heat from the furface of the earth, thofe countries would be warmeft which enjoyed the greatest quantity of fun-fhine. The British islands are fhrouded in clouds nine months of the year; yet our climate is milder than that of the fame parallel on the continent, where the fky is generally ferene. The elevated town of Quito, expofed to a brilliant fun, enjoys a temperate air; while the Peruvian plains, fhaded with fleecy clouds, are parched with heat. Were the reafoning in the text to be admitted, we should conclude, that the tops of mountains are warmer than their bafis. To fay that air, much rarefied, is not fufcep tible of heat, is a very extraordinary affertion, fince we are acquainted with no fubftance whatever that may not be heated Befides, a more intense cold may be artificially produced than what prevails in the lofty regions of the atmosphere, We must recur to other principles for the true folution of the fact. It is indifferent what portion of the air firft receives the heat; the effect depends entirely on the nature of its diftribution. If the atmosphere were of an uniform density throughout, the heat would, at all heights, be likewife the fame. But as the denfity varies according to the altitude, the diftribution of heat is affected by that circumftance, and follows a certain correfponding law. I would gladly develope the principles from which this theory is deduced, but the popular nature of the prefent treatife forbids all abstract difcuffion. I fhall therefore, content myself with gi ving a table of the diminution of heat at different altitudes.

Altitude in feet.

3,000

6,000

9,000

12,000

15,000

18,000

21,000

Diminion of heat, in degrees of
Fahrenheit,

120

24

38

53

68

86/

944

The diminution of heat, on the afcent, is not quite fo great in extenfive continents ; for the intercourfe between the rare and the denfe portions of the atmos phere is, in this cafe, neceffarily flow, and the heat, which is principally formed at the furface, will only be partially dispersed.

It is a common mistake to fuppofe, that the fame heat obtains, at a certain depth, in every part of the globe. The fact is, that heat, originally derived from the fun, is communicated very flowly to the matter below the furface, which, therefore, does not feel the viciffitude of feafons, but retains the average temperature of the climate for many ages. Hence the utility of examining the heat of fprings which is the fame with that of the fubftances through which they flow.

The

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