Liyury from Cold During Growing Period. 123 
or case (Fig. 59). The bulb of one thermometer is inclosed 
in thin muslin, which is wet just before using the instrument, 
by dipping the bulb in rain water. By means of a string 
attached to the board or case, at the end 
opposite the bulbs, the instrument is 
whirled about in the air a few times, after 
which the thermometers are quickly read 
and the difference in the readings noted. 
ip 
: 
i 
J 
| 
UJ 
a 
a 
HI 
‘a 
a), 
Hi 
HI 
8) 
a 
a 
a 
H 
a 
a] 
L] 
4 
a 
a] 
a 
When the air is comparatively dry, evapo- 
ration from the muslin proceeds rapidly, 
and, on account of the heat absorbed, the 
wet bulb indicates a lower temperature 
than the dry one. When the air is damp, 
evaporation is slower, and the difference 
between the readings of the two thermom- 
eters is less. In saturated air, evaporation 
ceases and the two thermometers read 
Fie. 59. Sling psy- : ; 
chrometer, used to alike. By means of the following table, 
Se Si ie the dew point for any ordinary out-door 
temperature and atmospheric humidity may be readily 
determined. 
Table for computing the Dew Point in Degrees Fahrenheit. 
Dry WET BULB DEPRESSION. 
1 YI: Se ee | ots PEs eet TS 
—1—12 —32... 
37 34 32 29 25 21 19 15 yk: aed Ale Ree 
388 35 33 30 26 23 19 17 11 +6—3 —16 a 
89 36 34 31 28 24 20 16 14 8 0 —11 —8l 
40 37 33 32 29 26 22 18 12 10 + 3 — 6 —22 
41 39 36 33 30 27 23 19 14 8+6—2—15 ... 
42 40 37 34 31 28 25 21 16 100 + 3 —2 —9 —29 
4% 41 38 35 33 30 26 22 18 13 +6 —3 —5 —20 
44 42 39 37 34 31 27 24 20 16 9 —1 —12 —18 
45 43 40 38 35 32 29 25 21 17 oll +4 —7 —27 
