28 C> 
SECOND REPORT- 1832. 
noting the distillations in given times by ascertained differences 
of temperature. 
The instrument is filled with ether in the same manner as 
Wollaston’s Cryophorus (from which the suggestion was taken); 
but there is an inconvenience, arising from the circumstance of 
the difference of pressure under which the instrument is her¬ 
metically sealed, which renders two instruments not strictly 
comparable; this he proposes to remedy by sealing a standard 
instrument when exhausted to a known pressure by the air 
pump. 
The ether or sulpliuret of carbon employed must be per¬ 
fectly pure , or there is a re-absorption. The circumstance of 
being exposed to the air, or covered, makes great differences in 
the indications ; especially in windy weather. To avoid an in¬ 
conveniently long scale, there should be two instruments con¬ 
structed, one for winter, and the other for summer. The Pro¬ 
fessor has kept for nearly a year a register of sunshine. 
b. ) Refle. vion of solar heat. 
1. ) It takes place exactly by the same laws as that of the 
light. 
The heat is collected in the focus of concave reflectors along 
with the light. 
2. ) The sun’s rays reflected from the moon, are probably 
much too feeble to allow of any heat being made sensible. 
Dr. Howard however states, that with a peculiar differential 
thermometer he has obtained an effect. (Sillimaris American 
Journal, vol. ii. 329.) 
MM. Melloni and Nobili(with the apparatus before described) 
tried to detect heat in the moon’s rays, but without success; they 
mention however that terrestrial radiation interferes greatly with 
such experiments, and do not describe fully their contrivances 
for obviating this cause of error. ( Ann.de Cliimie , Oct. 1831, 
p. 210.) 
3. ) Berard (Memoir before cited,) tried the polarisation of the 
solar heat; that is, polarized the sun’s light; and in the position 
of non-reflexion found that the heat had disappeared with it. 
(See Edinh. Journ. of Science, vi. 297.) 
c. ) Under this head nothing known. 
d. ) Effect of surface on the absorption of solar heat. 
1.) I am not aware of any experiments directly showing how 
