46 Prof. Marcet on the Variations of the Temperature, &c. 
ethrioscope as shewing the intensity of terrestrial radiation, 
and the increase of heat which takes place in certain circum- 
stances in proportion as we ascend. I shall not, however, enter 
at present into any detail of the observations I made on this 
subject ; because, hitherto, they do not appear to me to have 
led to any decisive consequence. But the general result of 
them is, that the variations manifested in the increase of the 
temperature of successive strata of the atmosphere, in different 
cases, when the night appeared equally clear and serene, have 
not coincided in a striking manner with the corresponding va- 
riations remarked in the intensity of terrestrial radiation, as the 
latter is indicated by the ethrioscope. Thus, I have often ob- 
served the liquid indicator of this instrument denote the same 
intensity of radiation during a clear summer night, when the 
increase of temperature upwards did not exceed 2° or 3°, as 
during the same kind of weather in winter, when the same 
increase amounted to 4° or 5°. And even the less important 
variations which manifested themselves during the summer 
from one day to another, in weather to all appearance equally 
cali and clear, were not always accompanied by a correspond- 
ing change in the indications of the ethrioscope. There are 
probably other circumstances besides radiation, which have an 
influence on the phenomenon in question ; and it is only when 
these have been studied consecutively, that a determinate 
opinion can be formed on this subject. 
The results of the observations described in this Memoir 
seem to lead to the following conclusions :— 
1s¢, The increase of temperature in successive strata of the 
atmosphere as we ascend, and which is remarked at the time 
of sunset, however variable it may be either in regard to its 
intensity or its limit in reference to elevation, is a constant 
phenomenon in every state of the sky, except in the case of 
violent winds. 
2d, The time of the maximum of this increase is immediately 
after sunset ; from that moment it is stationary, or even pretty 
frequently diminishes, particularly when the dew is plentiful. 
At sunrise, the increase is, for the most part, not so conside- 
rable as at sunset. 
3d, The limit of elevation to which this increase of tempe- 
rature extends, seems rarely to surpass the height of 100 or 
