1914] HASSELBRING—EFFECT OF SHADING 267 
TABLE IV—Continued 
HYGROMETER SLING PSYCHROMETER 
FoR 24 HOURS ENDING 
P.M. 
: Open Shade Difference Open Shade Difference 
January ne aes 7 80.5 +3.5 50.8 57.8 +7.0 
CN Nie 76.5 80.0 +3.5 48.4 58.2 +9.8 
: “Ltn See aes 80.0 83.0 +3.0 ge 66.4 +9.2 
A Seige teaae 78.5 82.5 +4.0 so.8 62.8 +4.6 
a5... 76.0 80.0 +4.0 50.2 54.4 +4.2 
pe -86..5..... 77.9 80.5 +3.5 52.0 60.0 +8.0 
i canoe 77.0 80.0 +3.0 53-8 56.8 +3.0 
ee 78.5 +4.5 50.0 54.8 +4.8 
were readjusted only once during the entire time. To overcome 
the effects of accidental differences not detected the hygrometers 
of the two stations were interchanged each week. From what has 
been said it will be clear that only a relative value can be ascribed 
to the humidity records. Since the two instruments agreed with 
_ €ach other when kept under the same conditions, this record, 
nevertheless, ought to give a fair idea of the differences in relative 
humidity inside and outside the tent. The daily averages were 
obtained by integrating the curves of the records (which are on 
circular charts) by means of a Bristol-Durand radii-averaging 
Instrument. These averages, together with the differences between 
the figures for the two stations for each day, are given in table IV. 
In addition to the hygrometer records, daily observations were 
taken at noon in the two stations by means of a sling psychrometer. 
The results of these observations are given in the fourth and fifth 
columns of the table, where each figure represents the average of 
five readings. These observations taken at noon represent approxi- 
mately the lowest relative humidity for each day. 
Table IV shows that the relative humidity is higher inside than 
Outside the tent, but the difference is not as great as that found 
by Stewarr in Connecticut. Owing to the greater quantities of 
water given off by the plants with increase in leaf surface during 
Stowth, the difference is greater toward the end of the season than 
at the beginning. This relation is brought out still more strikingly 
by the differences during the day, when the plants are actively 
'ranspiring. The difference in the relative humidity inside and 
