SUPPLEMENTARY REPORT ON METEOROLOGY. 63 
1838, printed in the Comptes Rendus*, and also privately cir- 
culated. 
69. A question of very great importance in meteorology, and 
one of the first which radiation experiments were employed to 
determine, is the proportion of incident solar heat which is 
absorbed in its vertical passage through the atmosphere. In 
the acute, learned, and original work of Lambert on Photo- 
metry, published in 1760, (and now, I know not why, extremely 
scarce,) this question is fully discussed; formule are investi- 
gated for the total loss of light at any altitude, according to an 
assumed law of density, (which had already been done by Bou- 
guer ft, who first suggested the method,) and from a comparison 
of intensities at two elevations, the total loss in the atmosphere 
by a vertical transit is ingeniously deducedt. From experi- 
ments made at Coire with blackened thermometers, Lambert 
deduced the loss of light or heat by a vertical transit through a 
clear atmosphere to be about ;4ths of that incident on the ex- 
terior boundary§. Bouguer had estimated the loss of light at 
only one half as much. ; 
70. Laplace || investigated the law of extinction of light in the 
atmosphere, and showed that it may be made to depend ap- 
proximately on the measure of refraction at any angle, bya very 
simple formula. He employed Bouguer’s constant for 0° of 
zenith distance. ; 
71. Sir John Leslie made experiments on the principle of 
Bouguer and Lambert, with his photometer placed in a position 
which equalized as much as possible the cooling causes, and 
admitted the direct heat of the sun4. The results are con- 
tained in the article Climate, in the Encyclopedia Britannica, 
from which it appears that he estimates the loss of heat by 
absorption at {th of that vertically incident. 
72. Professor Kamtz, who has done full justice to Leslie’s ele- 
* Mémoire sur la Chaleur Solaire, sur les pouvoirs rayonnants et absorbants 
de l Air Atmosphérique, et sur la Température de l’ Espace.— Comptes Rendus, 
vii. 24, 
t+ Traité d'Optique, &. 4to. 1760, p. 306. Bouguer restricted his method 
to Be cioparicon of the intensity of lunar light at different elevations with wax 
candles, 
t Lambert, Photometria, sive de Mensura et gradibus Luminis, Colorum, et 
Umbre, p. 392, &c. 
§ Photometria, p. 397. Compare Pyrometria, § 283. 
|| Mécanique Céleste, iv. 282. 
{] Sir John Leslie himself gives no account of the circumstances under which 
the observations were made, but I learn from his assistant, that the photometer 
was placed under the revolving dome of the Edinburgh Observatory, the slit 
being turned towards the sun, and that it was observed very frequently at dif- 
ferent hours. 
