384 Proceedings of Societies. [May, 
“ On the Relation existing between the Duration of Sunshine? 
the amount of Solar Radiation, and the Temperature indicated 
by the Black Bulb Thermometer in vacuo," by G. M. Whipple, 
B.Sc., F.R.A.S. The author has instituted a comparison be- 
tween the duration of sunshine, as determined by Campbell’s 
sunshine recorder, and the amount of solar radiation, as ascer- 
tained from the readings of the black bulb thermometer in vacuo , 
for the year 1877 , at the Kew Observatory. It is evident that 
there is a close relation between these phenomena, but, owing to 
the great range of the black bulb thermometer, the exadt nature 
of the connection is not immediately evident. The author says 
that it may be safely concluded that the measure of solar radia- 
tion, as given by the black bulb thermometer, is only to be consi- 
dered at any place as an indication of the relative presence or 
absence of cloud from the sky at the locality, and so its use as a 
meteorological instrument may with advantage be set aside in 
favour of the sunshine record, which has not the elements of un- 
certainty attached to it, inseparable from the former instrument. 
March 19. — Mr. C. Greaves, President, in the chair. 
The papers read included one on “ Dew, Mist, and Fog,” by 
George Dines, F.M.S. The author has, during the last two years, 
made a number of experiments to determine the amount of dew 
that is deposited on the surface of the earth. The plan adopted 
was as follows : — Glasses similar to ordinary watch-glasses were 
procured ; the surface area and the weight of each was ascer- 
tained. These glasses were exposed to the open air in the 
evening, being placed on different substances, viz., on grass, on 
slate, and on a deal board, the two latter being raised a few inches 
above the grass. A minimum thermometer was generally placed 
by the side of each glass. It is only on rare occasions that an 
amount of dew exceeding o*oio inch in depth has been deposited 
upon the measuring glasses, and out of 198 observations in only 
three has that amount been exceeded : 58 observations give the 
amount from o*oio to 0*005 i nc h, 107 from 0*005 t0 0*001 inch, 
22 less than o*ooi inch, and 8 observations no dew at all. The 
author thinks it may be fairly assumed that the average annual 
deposit of dew upon the surface of the earth falls short of 1*5 inch. 
There are two kinds of mist, the morning and evening. The 
morning mist is caused by the evaporation from the water and 
the moist ground taking place faster than the vapour is taken 
away ; the air becomes saturated, but this does not stop the eva- 
poration ; the vapour continues to rise into the air, is there con- 
densed, and forms mist, which gradually spreads over a wider 
surface. The evening mist is produced as follows : — The cold 
on the grass, caused by radiation, lowers the temperature of the 
air above it ; the invisible vapour of water previously existing in 
the air is in excess of that which the air can retain when the 
temperature is lowered ; the surplus is condensed, becomes a 
