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>GUUE 
A CONTRIBUTION TO THE STUDY OF EVAPORATION 
FROM WATHR-SURFACES. 
By J. R. SUTTON, M.A. 
(Prare IX.) 
[COMMUNICATED BY PROF. J. JOLY, F.R.S., HON, SEC. ROYAL DUBLIN SOCIETY. | 
[Read, Novemper 21; Received for Publication, Novemprr 23, 1906; 
Published, Frsruary 21, 1907.] 
Most of the observations and experiments described in this paper 
were commenced with the idea of testing a number of previous 
results made by others, which have been published with some 
confidence and apparently favourably received. They are also, 
to a certain extent, a development of some previous work of my 
own.’ The climate of the table-land of South Africa is very 
favourable to work of this sort, on account both of the great 
average rate at which water evaporates in the open air, and also 
of the much wider range of moisture conditions than is to be 
usually met with elsewhere. The whole of this paper refers to 
experiments made under meteorological conditions, that is to say, 
under the open sky, or in louvered screens, the water-surfaces being 
warmed or cooled by contact with the air alone. In this respect 
the circumstances of the investigation differ entirely from the 
usual product of the laboratory, in which the usual (and fatally 
defective) way of increasing the “evaporation” from a water- 
surface is to heat it from below over a stove or lamp. 
The principal instruments employed here have been :— 
1. A Piche atmometer of the usual form, in which water is 
evaporated from a moistened surface of porous paper. It is 
assumed that the evaporation is equal from equal areas all over 
the exposed part of the paper dise above and below. The tube is 
graduated on the glass to equal volumes, and the factor required 
1 See, e.g., J. R. Sutton, ‘‘ Results of some Experiments upon the Rate of 
Eyaporation,”’ Trans. South African Phil. Soc., 1903, xiv., Part 1: ‘‘ Results of some 
further Observations upon the Rate of Evaporation,’’ Report of the South African 
Association for the Advancement of Science. 1904. 
SCIENT. PROC. R.D.S., VOL. XI., NO. XIII. q 
