1895. ] Recording Apparatus for Transpiration. 475 
starting point. Here the crescent nut will again pass into 
the thread first followed, and again carry the sleeve across the 
screw. The reciprocating motion of the pen thus secured is 
strictly in a straight line, and the subdivisions of the scale of 
the record sheet are equal throughout, conditions that are ex- 
tremely desirable, especially in a recording rain gauge where 
rate of rainfall is to be obtained.” 
e equal subdivisions of the scale thus obtained also 
greatly facilitate the determination of the rate of evapora- 
ion 
The record sheet is divided into hours by lines running 
parallel to the axis of the cylinder; the hours are subdivided 
into spaces of ten minutes. Lines representing grams are 
drawn at right angles to the hour lines. The value of these 
spaces can be regulated by varying the weight of the counter- 
poise on the balance. Our instrument is set up so that each 
space equals one gram. One movement of the armature car- 
ries the counterpoise a distance equal to one-tenth of a gram 
and the pen at the same time moves across one-tenth of a 
gram space on the record sheet. Once across the sheet 
equals fifty grams. When the pen has recorded this amount 
it passes back, making the record in the other direction as be- 
fore explained. 
elow is shown a record of evaporation from a fuchsia from 
12 M. March 16thto 12M. March 18, 1895. It is one sheet of 
U. S. Department of AGmtCucrure: pirgin o Vermble rman wh Paley. 
St 
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a continuous record for the month of March. The pen was 
started at 12 M. March 16th atthe top of thesheet. From 12 
M. to 1:25 P. M. the loss wasat the rate of one gram for each 
ten minutes. During this time the plant was exposed to 
direct sunlight. At 1:25 a screen was placed between the 
Plant and the sun. The rate of evaporation was greatly 
