90 M. POUILLET ON SOLAR HEAT, ETC. 
hours of the day : its central thermometer then assumes consider- 
able elevations of temperature; it often rises to 50° above the 
ambient temperature towards noon, and it sometimes even rose 
to 90°, the temperature of the air being 27°, which gives an ele- 
vation of 63°. I point out these results only to show, on the one 
hand, that the actinometer might be graduated by the pyrhe- 
liometer, if we only desired to have approximate results of the 
solar heat; and to show, on the other hand, that thermometers 
exposed to the sun may, according to the dispositions given 
them, take any required excess above the temperature of the air 
from 3° or 4° up to 63° or 64°. 
