* 
H, A. Hazen—Thermometer Exposure. 369° 
form of dry and wet bulb “fronde” was devised, which has: 
been in constant use since and has given good satisfaction. 
The thermometers were lashed together, the stem of one two 
inches longer than the other, in such a manner as to bring the 
wet bulb about two inches below the dry. This permits of im- 
mersing the wet bulb without wetting the dry. A few swings 
only are needed in making an observation, it is swung perhaps 
forty or fifty times, then read, swung again and read, ete., it 
brought in contact with a large mass of air it must give its tem- 
perature unless the results are vitiated by other causes. It has 
been objected, for example, that friction with the air will tend 
to raise the temperature, and that the centrifugal force will on 
‘the contrary tend to depress the mercury column. Repeate 
Ment, when the air was still or had very little motion, with the 
result that at midday with a clear sky, in the summer time, the 
temperature given by “fronde” may be ‘7 to 10 degree 
higher in the sun than in the shade. It cannot be considered 
however, that such a shade temperature as was used represents 
the exact air tem perature, but it was nearly correct, perhaps the 
true value of the air temperature was somewhat higher, and 
that the effect of the sun heat is a little less than 07°, : 
ince a thermometer exposed to the clear sky reads at times 
One degree lower than if sheltered, we might conclude that the 
“fronde” will be liable to the same effect unless entirely over- 
