Mr Rowell on the Phenomena of Evaporation. 53 
on the volume of water, as only the particles on the surface 
of the water can obtain their coating of electricity. 
Wind increases evaporation by assisting the particles of 
vapour to separate from the body of water, thus enabling the 
particles to obtain their full coating of electricity, which they 
cannot have while resting on the surface of the water. 
Evaporation from ice is owing to the coldness and dryness 
of the air separating the minute particles at the surface, 
when obtaining their coating of electricity, they are rendered 
sufficiently buoyant to be carried off by a brisk wind. 
Evaporation from ice, snow, or even water, at very low 
temperatures, is trifling except during windy weather. 
Evaporation in vacuo (¢. e. under an exhausted receiver) 
is from the weight of the atmosphere being taken off, when 
the particles ef water are buoyed up one upon another by 
their electrical coatings.* 
* The following extracts from the Philosophical Magazine, January 
1842, will shew the agency of electricity in evaporation :— 
*« The following experiment was made to prove that evaporation 
would not go on so freely from an insulated vessel as from an uninsu~ 
lated one :— 
“In a warm room, over an oyen in daily use, I suspended, by silk 
threads, two shallow vessels, eight inches and a half in diameter, con- 
taining eight ounces of water each ; a small copper wire was hung from 
one vessel to the earth to take off the insulation, both vessels being simi- 
larly suspended in every other respect. After being suspended 26 hours, 
the insulated vessel had lost 2 oz. 11 dwts. and 15 grains ; and the other 
vessel, 3 oz. 6 dwts.; shewing an excess of evaporation from the non-in- 
sulated one of 14 dwts. 9 grains. 
“ J have tried similar experiments with water placed in the rays of the 
sun, and, on all occasions, the evaporation has been greatest from non- 
insulated vessels. There is a difficulty in obtaining correct calculations 
from the above experiments, as it is scarcely possible to keep up com- 
plete insulation from electricity ; and the vessel of water must have its 
proportion of electricity when placed in an insulating situation, which 
will assist the evaporation for some time ; but I believe, if complete in- 
sulation could be obtained, and a vessel left without any electricity, 
that no evaporation would go on at moderate temperatures.” 
It has long been well known that evaporation is increased by water 
being charged with electricity: this increase was attributed to the par- 
ticles of water being repelled from the surface, as any light substance is 
