372 Hl. A. Hazen—Thermometer Exposure. 
known conditions which are slowly changing, will enable us to 
follow effects due to gradually rising or falling temperature, 
the increase or decrease of wind velocity, the shifting of the 
wind, slowly changing humidity, etc. 
The following are a few of the results collected from the 
observations since September 1, 1883. 
To determine the least size of a shelter necessary to over- 
come the effects of heat from the sides, there were arranged 
Table II shows the results of these observations. 
Considering the difficulty of comparing thermometers hung 
side by side in free air, the accordance of these results is very 
satisfactory. In the morning there is a mean difference of 1'8° 
between the east and west sides; a fall of °55° or nearly 4 the 
whole amount, in the first 9 inches, and one of 1:2° or $ in 
the first 18 inches. In the afternoon there is a fall of 15° 
thermometer exposed on the outside of “ Pattern. 
olumn 1 gives the mean time of each set or of five succes- 
sive observations, the next five columns give, the dry and wet 
thermometers, the relative humidity from these, the black 
thermometer and the difference between this and the dry, 1? 
A); the next five give the same values for (B); the next five 
for (C); the next three give the dry and black and their dif- 
