26 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—IQ22 
of two mercury thermometers mounted side by side in a white box. 
The bulb of one was white and of the other, black. The readings 
were recorded as the percentage of the maximum difference observed 
during the season of 1920, this maximum being taken arbitrarily as 
100 per cent. 
Temperature measurements were made by means of mercury 
thermometers. A white bulb mercury thermometer was used for meas- 
uring air temperature in the sun. An interesting comparison of un- 
covered mercury, white, black, and red spirit thermometers is shown 
im Table I. 
Table I. Comparative Readings of Thermometers with Differently Colored Bulbs 
Taken at I p.m. 
Light Light Light Light Light 
Color of intensity intensity intensity intensity intensity 
bulb 52% 20% 75% 72760 55% 
Aug. 31 Sept. 1 Sept. 2 Sept. 6 Sept. 7 
IIRC =5 shes cae, “RS E Ae AC. AlOy “1G, AG) AC 40) 3€ 
IRA SLGM A Seto sia soy AC 28.5316 B8:5.C Mi AG 20.5€ 
Mercury Sra... gis AE 26555 Cee ep AE ey GC, Says (C 
WVilnite ey cecrec aahea(© Bie AS 27 mG aa EC 320, -€ 
Subcortical temperatures in the logs were measured by mercury 
thermometers inserted in a hole bored into the end of the log just 
beneath the bark. 
The evaporating power of the air for each 24-hour period was 
measured by means of Livingston porous cup atmometers. The white 
spherical type was used. An average of readings from three cups 
was taken for each set of logs. Since these instruments were left in 
position during the entire season, it was necessary to equip them with 
check valves to prevent the absorption of water during rains. A single 
mercury valve mounting proved very satisfactory and caused little 
trouble. A special mounting was designed for measuring the rate of 
evaporation at any particular time. In this mounting the evaporation 
during one minute was measured in a graduated capillary tube and 
the rate per hour calculated. 
Relative humidity was measured by the use of the cog psychrom- 
eter (Clements 1905). This instrument has proved very satisfactory, 
as it is accurate and easily operated in a limited space. 
Measurements of the moisture content of the cambium and outer 
sapwood regions were attempted by running moisture analyses of sam- 
