Oct. x 8 , 1915 
Automatic Transpiration Scale 
121 
Fig. 6 .—Schematic diagram of Blackmail and Paine’s recording tran- 
spirometer, in which water is automatically added to the pot to offset 
the transpiration loss, so that the moisture content of the soil is kept 
uniform. 
tained in a floating cylinder a, which rises as the load decreases and 
traces its movement on the smoked drum of a clock. Like other appa¬ 
ratus involving the 
principle of flotation, 
this apparatus is sub¬ 
ject to errors arising 
from changes in buoy- 
a ncy accompanying 
changes in tempera¬ 
ture. 
A transpiration bal¬ 
ance devised by Rich¬ 
ard Fr&res (Burger- 
stein, 1904, p. 8-9) is 
illustrated in figure 8. 
The balance is made 
very insensitive by a 
heavy bob. The 
movement of the bal¬ 
ance pan from the “down" to the “up" position corresponds to a known 
loss in weight, depending on the weight and position of the bob. The 
movement of the beam Is recorded 
directly on the drum of a clock. 
Copeland (1898) has described an 
apparatus (fig. 9) for recording tran¬ 
spiration in which the weight of the 
plant is balanced over a pulley by 
the weight of a partially submerged 
hydrometer bulb. The pulley shaft 
rolls on plate-glass supports to re¬ 
duce the friction. A tracer sup¬ 
ported from a second wheel records 
the motion on smoked paper on a 
clock cylinder. With its maximum 
load (3.5 kgm.) the instrument re¬ 
sponds to a change in weight of 
0.05 gm. 
Corbett (1900) has used a large 
Nicholson hydrometer for measur¬ 
ing transpiration, the plant being 
placed directly on the pan a of the 
hydrometer b (fig. 10). The appa¬ 
ratus is made self-recording by con¬ 
necting the float with the lever of 
an auxanometer. This apparatus, like that of Copeland, is affected by 
temperature, which changes the density of the water and consequently 
Fig. 7.—Krutizky’s potometer for recording tran¬ 
spiration, in which the loss from the potometer is 
continuously replaced from the supply in the 
floating cylinder. 
