H. A. Hazen— Thermometer Exposure. 365 
Art. XLITL—Thermometer Exposure; by H. A. HAZEN. 
[Read before the Philosophical Society, Washington, D. C., October 13, 1883.] 
THE subject of thermometer exposure may be discussed under 
two general divisions. The first of these relates to the locality 
_ Many large region where the thermometer shall be exposed, in 
order that it may give the true air temperature of the locality. 
The second relates to the immediate environment of the 
thermometer which shall fulfill the same requirement. 
Of local heat effects; character of ground, ete., are all import- 
ant. A creat diversity of opinion relative to many of these 
& low level, and moreover, unless exposed on the summit of 
hill, there will be danger of an interruption to the wind, so 
that in hot, nearly calm weather the air will become stagnant, 
thus Vitiating the result we seek. For example, mean monthly 
44 feet above 
ed uotable exceptions, for example, the following: table ex- 
bits the mean relative humidity for four months’ observa- 
tions. 
Relative humidity at various heights. 
Month. 19 Meters. 15°9 Meters 26°83 on 
June, 1873  63°3¢ 59°0% 
uly, : ena 62-0 60-7 
June, 1874, 576 ! 56" 557 
July, 721 T1'4 76°2 
It seems impossible to explain these peculiar results which 
lo not follow any law with respect to height; on the whole, 
however, the humidity has a tendency to increase with ap- 
_ Proach to the earth’s surface. 
