of the Lower Strata of the Atmosphere. 35 
ly perceptible. These experiments were again renewed, in 
1784, by the English natural philosopher Six. This observer, 
_ having compared, for a considerable length of time, the tempe- 
rature of three thermometers, one of which was placed at the 
foot of Canterbury Cathedral, the second on the top of the prin- 
cipal tower of that edifice, at a height of about 200 feet, and the 
third at an elevation of 110 feet, states, that he has often re- 
marked a difference of from 5° to 6° between the two first 
thermometers during calm and clear nights, and an interme- 
diate temperature at the station of 110 feet. When the wea- 
ther was cloudy, the temperature appeared to him to be nearly 
the same at the three stations; if there was any difference in 
them, it was the reverse of what had taken place in clear wea- 
ther, that is to say, the thermometer near the earth stood 
higher than that at 200 feet. White, in his Natural History 
of Selbourne, has likewise noticed a difference of from 5° to 
6°, and on one occasion a difference of 10° between the tem- 
perature of the plain and that of a neighbouring hill about 
200 feet in height. 
Leslie says, he has remarked* that, in England, about two 
hours after sunrise, the ground is of the same temperature as 
the stratum of the atmosphere in contact with it.t From that 
time till two o’clock in the afternoon, the ground is warmer 
than the contiguous atmosphere. After two o’clock, this differ- 
ence diminishes until about two hours before sunset, when the 
ground again becomes colder than the surrounding air. This 
difference, the author adds, goes on increasing during the 
night. 
Finally, Wells, in his essay on Dew, published in 1814, has 
observed that in calm and clear nights, the air at the height 
of four feet most frequently exceeded the temperature of the 
ground from 3 to 4 degrees, and sometimes from 5 to 6 degrees. 
From all these observations taken together, the two follow- 
ing facts seem to result: 1s¢, During calm and clear nights, 
* Trans. of the Royal Society of Edinburgh, vol. viii. On Impressions of 
Cold, ke. 
t The remark appears general ; the author does not apply it solely to calm 
and clear weather. 
ms, 
