58 grains, 22 grains of pure gold, and 1 43 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. I much regret not having been present when the work was going on, that I might have feen 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 subsequent diligent infpection of the feveral veins that range through the mountain, might aflift towards the difcovery of that from whence it was detached. I fhall fhortly return to England; and on my arrival, will fend fpecimens of the gold, and of the different fubftances of the mountain, to be depofited (if you think proper) in the collection of the royal fociety. And am, with great refpe&t, &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 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 cavities. This opinion was difcovered to be well founded, by cutting through fome of the fmall 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, of fine gold; 21 of fine filver; 1 of alloy, which feemed to be copper tinged with a little iron. The fecond fpecimen differed only in holding 21 inftead of 21% of fine gold. Major John Brown, of the royal engineers, tranfmitted to the right hon. Thomas Pelham, a fketch of the fpot where the gold was found, which Mr. Pelham has obligingly permitted to be engraved, for the ufe of the royal fociety. C. B. we should feel the fame degree of cold in all regions, after we have rifen to a certain height, fay 24,000 feet; confidering that the variations with refpe&t to heat, on the carth, not only in the different climates, but in the fame country, at different feasons 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 firft 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 respect to us, and even far beyond the height of the loftieft mountains, is a mere aothing, compared to the distance of the fun. which is about thirty millions of mites*. This is therefore, a very important difficulty, which we must 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 transparent than others. One of thefe tranfparent bodies being expofed to the fun, is not heated to fuch a degree as a body not tranfparent, as wood, iron, &c. Bodies not tranfparent are denominated opaque. A burning-glafs, for example, by tranfmitting the rays of the fua, fets on fire opaque bodies, while the glafs itfelf is not fenfibly beated. Water exposed to the fun becomes fomewhat warm, only bea caufe it is not perfectly tranfparent; 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 bottom, it has no preceptible heat, though the fun bears upon it. As air is a very tranfparent body, to a much higher degree than glafs 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 perfedly tranfparent: it is even fometimes fo loaded with vapours, that it lofes almoft entirely its transparency, and prefents only a thick fog. When the air is in this ftate, 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 tranfparent; and for this reafon the rays of the fun cannot immediately produce any effect upon it. This air is likewife too reniote Mr. Euler always menas German miles, of 4000 fathoms each, or fomewha ader 4 miles English.-E. 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 fuppofe 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 higheft 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, being very elevated, muft 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 muft contain lefs vapour and other particles which ufually 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, aud lower ftill, if it were ftill 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 furfice 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 refpecting confiderable heights. This elucidation will, I fatter myfelf, prove fatisfactory+, Account There are clouds, however, above thefe mountains, and in almost as great a quantity as above the plains, which is demonftrated by the inows which cover the highest 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, muit be attributed almost entirely to the tranfmiffion of the water which found itself diffolved in the air, under the form of elastic Buid, to a liquid ftate. The heat of the folar rays, intercepted by the cloud, can produce no change in the inferior temperature, as it would have been tranfimitted from the ground.-F. E. The reafon which profeffor Euler affigns for the coki that prevails in the higher regions of the atmosphere feems plauble, but will not stand an accurate xamination. Light is much impaired in its pallage through the atmosphere, C and ATURAL HISTORY cation of heat ftrial bodies, to at the farface of the earth, as it is that the air there must be as hot as only upon contiguous, on all fides, to opaque Hence you bodies, on which the rays of the the rays fun fall. The objection is 64; ef and no folution can be given but we fhould feel the fame degree of becomes fomewhat ere sud we know this. That the air at Quito, te- be of beat as common air, Antain Jefs vapour and which ufually float te, very much cbly fufcepri ere fubinia Nr of fuch a quality is not fo ..ced with no ..enfe cold may be ns of the atmosphere. n of the fact. It is indiffe c; the effect depends entirely on ofphere were of an uniform denfity But as the den s, be likewife the fame. the diftribution of heat is affected by that ain correfponding law. I would gladly develope the .neory is deduced, but the popular nature of the present act difcuffion. I fhall therefore, content myself with gi ninution of heat at different altitudes. de in feet. cern objects parent, pe Thefe be 3,000 6,000 amond. 9,000 nents; The diminution of heat, on the afcent, is not quite fo great in extenfive contifor the intercourfe between the rare and the denfe portions of the atmofphere is, in this cafe, neceffarily flow, and the heat, which is principally formed at the furface, will only be partially difperfed. 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 substances through which they flow. The found a large uncommon bird fluttering in the heath, but not wounded, which he brought home alive. On examination it proved to be Colymbus glacialis, Linn: the great fpeckled diver or loon, which is molt excellently defcribed in Willoughby's ornithology. Every part and proportion of this bird is fo incomparably adapted to its mode of life, that in no inftance do we see the wisdom of God in the creation to more advantage. The head is fharp, and fmaller than the part of the neck adjoining, in order that it may pierce the water; the wings are placed forward and out of the center of gravity, for a purpose which fhall be noticed here after; the thighs quite at the podex in order to facilitate diving; and the legs are flat, and as harp backwards almoft as the edge of a knife, that in ftriking they may eafily cut the water; while the feet are palmated, and broad for fwimming, yet fo folded up when advanced forward to take a freth ftroke, as to be full as narrow as the thank. The two exterior toes of the feet are longeft; the nails flat and broad refembling the human, which give ftrength and increase the power of fwimming. The foot, when expanded, is not at right angles to the leg or body of the bird: but the exterior part inclining towards the head forms an acute angle with the body; the intention being not to give motion in the line of the legs themselves, but by the combined impulse of both in an intermediate line, the line of the body. Moft people know, that have obferved at all, that the swimming of birds is nothing more than a walking in the water, where one foot fucceeds the other as on the land; yet no one, as far as I am aware, has remarked that diving fowls, while under water, impel and row themselves forward by a motion of their wings, as well as by the impulfe of their feet: but fuch is really the cafe, as any perfon may eafily be convinced who will obferve ducks when hunted by dogs in a clear pond. Nor do I know that any one has given a reafon why the wings of diving fowls are placed fo forward: doubtlefs, not for the purpose of promoting their speed in flying, fince that pofition certainly impedes it; The following table exhibits the average heat of places on the level of the fea, computed by the celebrated aftronomer, profeffor Meyer, for every five degrees of latitude. Latitude. O 5 10 IS 20 25 30 35 40 45 - 621 58 By comparing this table with the preceding, it is eafy to difcover, for any latitude, the altitude of the curve of congelation, or where the average temperature is 320.-E. E. but |