392] ANNUAL REGISTER, 1706. 
Acecunt of the Great Speckled Diver AS one of my neighbours was” 
or Loon. From Woite’s Natural. traversing Wolmer forest from 
ist?s Calendar. Bramshot across the moors, he 
found 
and the heat communicated is in every case proportional to the quantity of absorp- 
tion, It appears, irom some ingenious experiments of Mr. Bouguer, that we re- 
ceive only four-fifths cf the rays of a vertical sun; and when that luminary ape 
proaches the horizon, the portion ef this light, which reaches the surface 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 sun-beams are most powerful on the summits of lofty mountains, for they sufe 
fer the greaiest diminution in passing through the dense air of the lower regions< 
If the atr derived its heat from the surface of the earth, those countries would be 
warmest which enjoyed the greatest quantity of sun-shine. The British islands are 
shrouded in clouds nine months of the year; yet our climateis milder than that 
of the same parallel on the continent, where the sky is generally serene. The ele- 
vated town of Quito, exposed to a brilliant sun, enjoys a temperate air; while 
the Peruvian plains, shaded with fleecy clouds, are parched with heat. Were the 
reasoning in the text to be admitted, we would conclude, that the tops of moun-" 
tains are warmer than their basis. ‘To say that air, much rarified, is not suscep- 
tible of heat, is a very extraordinary assertion, since we are acquainted with no. 
substance whatever that may not be heated. Besides, a more intense cold may be 
artificially produced than what prevails in the lofty regions of the Gentethere: 
We must recur to other principles for the true solution of the fact. It is indiffee 
rent what portion of the air first receives the heat; the effect depends entirely on 
the nature of its distribution. If the atmosphere were of an uniform density 
throughout, the heat would, at all heights, be likewise the same. But as the den- 
sity varies according to the altitude, the distribution of heat is affeéted by that 
circumstance, and foilows a certain corresponding law. I would gladly develope the 
principles from which this theory is deduced, but the popular nature of the present 
treatise forbi’s all abstract discussion, I shall, therefore, content myself with giving 
a table of the diminution of heat at different altitudes. 
Diminution of heat, in degrees of 
Altitude in feet. Fahrenheit. 
3,000 — — _ — 120 
6,000 _ -- _ _ 24% 
9,000 Le we = = $8 
12,000 = ve als = 53 
15,000 ts = _ —_ 684 
18,000 — ae — _ 86 
21,000 — = = _ 94 
\ 
The diminution of heat, on the ascent, is not quite so great in extensive continents ; 
for the intercourse between the rare and the dense portionsof the atmosphere is, in 
this sateoneeetarily slow, and the heat, which is principally formed at the surface, 
will only be partially dispersed. t ; 
It is a common mistake to suppose, that the same heat obtains, at a certaig 
depth, in every part of the globe. The factis, that heat, originally derived from 
the, sun, is communicated very slowly to the matter below the surface, which, 
therefore, does not fec! the-vicissitude of seasons, but retainsthe average tempera 
ture of the climate for many ages. Hence the utility. of examinin the heat of 
springs which is the same with that of the substances through which they ere 
