1 28 Journal of Agricultural Research voi, v, No. 3 
circuit is controlled by the relay contact. The recorder is operated by 
a third circuit, B 3 , controlled by the tipping bucket on the ball valve. 
Each circuit is closed only momentarily, and the dry cells usually need 
to be renewed but once during the summer. 
AUTOGRAPHIC RECORDS FROM THE AUTOMATIC TRANSPIRATION 
SCALE 
The results of our transpiration measurements will be presented in 
other papers, but it seems desirable to reproduce here several daily rec¬ 
ords illustrating the actual performance of the apparatus. A word of 
explanation in con¬ 
nection with the in¬ 
terpretation of the 
records may be help¬ 
ful. The clock drum 
makes four revolu¬ 
tions during the day, 
so that the record is 
divided into four 6- 
h o u r periods. The 
pen is offset at the 
moment each ball is 
delivered. There are 
five such offsets or 
steps in one direction 
(up, for instance) and 
then five steps in the 
opposite direction. 
Since each offset cor¬ 
responds to a loss of 
20 gm. of water, the 
interval from the 
crest to the trough of 
the graph is the time 
required for the transpiration of 100 gm. of water, or from crest to crest, 
the time interval for 200 gm. loss. 
The wheat records shown in figure 16 were taken from a series ob¬ 
tained in 1912 inside the screened inclosure used in the water-requirement 
experiments. The normal wind velocity was reduced somewhat by the 
inclosure and by the proximity of other plants. The first record repro¬ 
duced (July 2, 1912) was obtained on a clear day. It will be noted that 
the time interval shortens as midday is approached—that is, the tran¬ 
spiration rate increases and attains its maximum value about 3 p. m., 
after which it falls rapidly. The transpiration at night, represented by 
Fig. 15.—Another view of the spring motor, showing the control mech¬ 
anism. When the magnet M is energized, the spring R attached to 
the armature T is pulled down, releasing the motor. Raising the 
beam de-energizes M, so that the motor, after making one revolution, 
is stopped by H again coming in contact with R. 
