Reduction of Transpiration Observations . 245 
meter served to show the extreme range of the temperate changes during 
the progress of an experiment. 
Observations were taken in three different localities: (1) in a ( dark * 
room with blackened walls, having a floor space of about 400 square feet: 
this room was chosen for its steady temperature properties, as the only 
portion of its walls which abutted on the external air was that occupied by 
a moderately large window ; (2) in a large room used as a general 
laboratory, well lighted from above, and with a floor space of about 600 
square feet ; and (3) in the open air. 
It is not necessary to give full details of all the figures obtained in the 
various experiments. One set of such figures may, however, be of interest 
as showing both the accuracy obtainable and the magnitude of the various 
quantities involved. They are the result of an experiment made under 
‘ dark 5 room conditions with the levels of the evaporating surfaces at the 
beginning of the experiment 0-7 cm. below the rims of the respective 
vessels, 1 and are given in Table I below. 
TABLE I. 
Mean height of barometer = 29"-6 (steady) 
Max. temp. = i8°-8 C. Min. temp. = i7°*7 C. 
Relative humidity — 63 per cent. 
d 
= 0-7 cm. 
k = 
o-oioi. 
n — 1 
-69. 
a . 
Log a . 
Time . 
Loss in 
weight . 
Log E 
(< obsd .). 
E 
( obsd .). 
E 
(, cold .). 
% error . 
cm. 
h. 
m. 
grm. 
0-5064 
10-17 
1-0073 
43 
4 
22-10 
i. 7 io 3 
o- 5 i 33 
-i -34 
8*26 
0-9170 
43 
0 
15-15 
i- 547 o 
0.3524 
o *3579 
+ 1*56 
7*°3 
0-8470 
42 
58 
11-90 
^4424 
0.2770 
0-2727 
-i -55 
5*^4 
07664 
42 
54 
8- 60 
1.3021 
0-2004 
0-1989 
- 0-75 
5.00 
0-6990 
42 
53 
6-45 
I * 1 774 
0-1504 
0-1530 
+ 1.73 
4*38 
0-6415 
42 
54 
5-25 
1-0878 
0-1224 
0-1224 
+ 000 
3*91 
0-5922 
42 
58 
4-373 
2-9977 
0-0995 
O-IOII 
+ i-6i 
3*30 
° , 5 I ^5 
42 
59 
3.286 
2-8835 
0-0765 
0-0758 
-0-91 
2*84 
o *4533 
42 
59 
2.422 
27510 
0-0564 
0-0589 
+ 4*43 
2-08 
0-3181 
42 
58 
1-484 
2-5384 
0-0345 
0-0348 
+ 0-87 
Average error regardless of sign = 1-47 per cent. 
In the above table, the first column gives the radii of the dishes used, 
the sixth column gives the rate of evaporation from each basin in grammes 
per hour as deduced from the data given in the preceding columns, whilst 
the seventh column gives the values of E as calculated from the equation 
E = 00101 a 1 ’ 69 . 
The constants in this equation were obtained, as explained above, by plotting 
the observed values of log E and log a against each other. It will be seen 
1 At the end of the experiment the values of d, calculated from the known values of the 
evaporation and the radii, in the above table were increased to 077, 0*77, 0*78, 0-78, 078, 
079, 079, o-8o, o?8o, o-8i cm. respectively. 
S 
