Marsh , and its Relations to Evaporation , &c. 3 1 1 
APPENDIX 
It was thought advisable to remove certain details respecting the 
evaporimeters used, the methods of calculating results, &c., from the paper 
itself, and to insert them at the end, in the form of an appendix. Such 
details do not affect the main argument of the paper, but may be useful to 
those who happen to be working at the same or cognate subjects. 
Calibration of the Evaporimeters. 
As stated in the foregoing paper, the evaporating surface of each 
instrument consisted of a porous earthenware cylinder. To prevent fluc- 
tuations in the area of this surface, in the event of the rubber corks being 
inserted to different depths on different occasions, the ends of the cylinders 
were made impervious for distances a little beyond those reached by the 
corks (see Text-fig. 3). 
Before filling, the cylinders were always first placed in water, and the 
air removed from their pores under an air-pump. 
It was also necessary to calibrate the instruments, in order that the 
results obtained might be comparable. The calibration methods were 
very much the same as those employed by Livingston. 1 The three instru- 
ments were compared with each other as follows : — 
(a) In a laboratory with windows facing the north: both doors and 
windows being kept closed. Direct sunlight was thus excluded, 
and air-currents reduced to a minimum. The three evapori- 
meters were arranged triangularly on a table, about 3 ft. 6 in. 
apart. In the centre was a crystallizing dish, filled with dis- 
tilled water to about 3 mm. below its upper edge. The free 
surface of water was at the same height as the centre of the 
evaporating surface of the cylinders. 
{h) The instruments were afterwards placed on the roof of the Botanical 
Laboratory at Cambridge. Here they were exposed to both 
sun and wind. 
In both cases readings were taken at intervals and in the laboratory the 
loss of water from the crystallizing dish was ascertained at the same time 
by weighing. After each reading the positions of the instruments were 
interchanged, in order to neutralize any differences due to the positions 
themselves. 
The respective evaporimeters may be designated I, II, and III : and 
as different porous cylinders were used during the second year, the year 
may be added. 
1 Livingston (’06), p. 26, 
