1911] LIVINGSTON—LIGHT INTENSITY AND TRANSPIRATION 421 
time period. One such device was available at the inception of 
this work, another was devised. 
1. The Hicks solar radio-integrator (obtainable from J. Hicks, 
Hatton Garden, London) consists of a glass vacuum chamber, the 
upper portion of which (a spherical bulb) is about half filled with 
dark-colored alcohol and exposed to the light. The alcohol vapor 
produced by the absorption of energy by the dark surface is con- 
densed in a lower bulb and collected in a still lower burette-like, grad- 
uated tube. The condenser and receiver are shaded during opera- 
tion, and readings are obtained from time to time on the amount of 
alcohol distilled into the tube. The instrument is occasionally to be 
inverted and the collected alcohol replaced in the exposed bulb, 
an operation made possible by a bent tube connection between 
the two bulbs. The rate of distillation depends of course on the 
difference between the vapor tension of the alcohol in the upper 
bulb and that obtaining in the shaded part of the apparatus. The 
shaded part nearly maintains the temperature of the surrounding 
air, while the exposed bulb tends to be warmed by the sunshine. 
Thus this instrument causes the sun’s rays to perform work in 
vaporizing alcohol and furnishes a means of measuring the work 
accomplished in terms of the amount of the liquid accumulating 
in the graduated tube. It is thus seen to be self-integrating. 
2. Various lines of experimentation had shown that the porous 
cup atmometer, a self-integrating device for estimating the evapo- 
rating power of the air (see Publ. No. 50 of the Carnegie Institu- 
tion), is measurably affected by sunshine; that, celeris paribus, 
it loses more water in direct sunlight than in shade. The differ- 
ence in rate so produced, however, is not as great as that observed 
in plants under the same varied conditions of illumination. Con- 
sidering this fact, it occurred to me that it should be possible to 
modify the porous cup in such manner as to cause it to absorb a 
greater proportion of the sun’s energy, and thus render the ratio 
of its readings in light and shade more nearly like those obtained 
from the plant. The instrument already integrates the influx of 
energy, in terms of the amount of water evaporated, and the con- 
templated alteration should involve only the coloring of the porous 
evaporating surface so as to increase its power to absorb radiant 
