Oct. i8 t 1915 
Automatic Transpiration Scale 
119 
that by offsetting the cylinder daily a weekly record could be obtained 
on one sheet. 
Transeau (1911), in working with xerophytes, employed hollow brass 
balls standardized to 0.4 gm. in place of tf-inch steel balls of 1 gm. weight, 
but states that the hollow balls are not as light as could be desired. The 
writers have found that ^-inch steel balls weighing 0.13 gm. can be 
readily used, provided the valve 1 is constructed to fit them. 
Woods (1895) used the automatic weighing rain gage of Marvin (1903) 
as a transpiration balance, the apparatus being modified to record loss 
instead of gain in weight (fig. 4). In this apparatus the counterpoise is 
Fig. 3.—Ganong’s automatic transpirometer in which steel balls are employed 
as weights. 
moved along the beam in -^-gm. steps by a screw actuated by an electro¬ 
magnet carried on the balance itself. The recorder (fig. 5) is independent 
of the balance. 
Blackman and Paine (1914) have recently described a recording 
transpirometer operating on the step-by-step principle, in which “water 
drops are used in place of steel balls, the water being added directly to 
the soil.” Their .apparatus has been represented schematically in figure 6. 
Water is allowed to drip continuously from a Mariotte system. During 
the greater part of the time the drops are intercepted by a movable 
1 For.description oi valve, see under “Ball-dropping device,” p. 133. 
5772°—15 - 2 
