594 
Proceedings of the Royal Society 
condition during that time. Preliminary observations with this 
instrument show that even in comparatively moist weather the 
total evaporation during twenty-four hours is great enough to be 
easily measured. 
The instrument is intended primarily to be used for determining 
the total evaporation from tanks and other free surfaces of water. 
Por this purpose it will be used first in connection with an atmo- 
meter, devised by Mr G. K. Winter and myself, by means of which 
we hope to determine with greater accuracy than has yet been done 
the total evaporation from the surface of a tank. By this means 
the constant of the hygrometer will be obtained, and future deter- 
minations can be made with the hygrometer alone. 
Other uses of the instruihent will at once suggest themselves, but 
it is not necessary to go into details till more complete observations 
have been made. 
Monday, ^th April 1884. 
EGBERT GRAY, Esq., Vice-President, in the Chair. 
The following Communications were read: — 
1. On the Philosophy of Language. By Emeritus 
Professor Blackie. 
2. On the Principles of Economics. Part III., Biological 
and Psychological. By Mr P. Geddes. 
3. Note on a New Eorm of Galvanometer. By Professor 
James Blyth. 
This instrument consists of a close spiral of insulated copper wire 
bent into the form of an anchor ring, so as to form an endless 
solenoid. The spiral is placed in a rectangular groove turned on the 
