1 1 2 Blackman and Paine. — A Recording Transpirometer . 
plants is thus recorded as readily as that of more active ones. The actual 
weight of water lost corresponding to each mark on the record must of 
course be obtained by weighing the appropriate number of drops. The 
solenoids are provided with ‘cut-outs’, so that the current only passes 
momentarily at the time the points first make contact with the mercury. 
The solenoids and recording pen can be readily worked with two 2-volt 
accumulators in series; the interposition in the circuit of a short piece 
of manganin wire is useful in adjusting the strength of current, so that 
March 8 March 9 
IO 12 2 4 6 8 IO 12 2 4 6 8 10 12 2 4 6 8 IO 12 2 
t+ri 1 1 1 1 1 HI 1 1 1 1 M 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 i 1 1 1 1 1 1 1 1 i+riihhiiithhr H 1 lii H+ ri tl t hl 1 1 
Clock record 
Transpirafion 
i titi i ti 1 1 1 1 in 1 1 ii n t 1 1 1 1 1 -wtmtH+H mi 1 1 1 1 H-mm-rni-t-nn 
Evaporation 
March 10 March 11 
_ /h . _ 
4 6 8 10 12 2 4 6 8 IO 12 2 4 6 8 IO 12 2. 4 6 
t-Htf H 1 1 1 1 1 1 1 1 1 1 1 1 i 1 1 1 1 1 1 1 ith 1 1 1 1 1 1 1 1 1 1 1 1 1 1 htrhttti l i H 1 1 I t l rtt l 1 1 1 1 1 1 1 i i tt+Ht 
Clock record 
tt m 1 I 1-1 I I li 111 I HUM 1 I' H 1 H-H I 1 -t— t-t- tl t 
Transpiration 
I 1 1 IN 1 1 I 
Evaporation 
Fig. 2. 
(The record has been cut into two and reduced to two-thirds.) 
the movement of the tubes is not too rapid. The rate at which the drops 
fall can be controlled by the tap, and should be rather slow, as the ‘ damped ’ 
balance is naturally somewhat sluggish in movement. Distilled or filtered 
water is preferably used in the reservoir to avoid any sediment partially 
blocking the tube. There is a certain loss of soil-water by evaporation 
through the glass tube, but it is very small in amount ; if necessary it can 
be measured and allowed for. A special thick-walled tube, ground flat at 
n 
t+ 
