181 
is acquainted with a gardener, who always Washes off the electric showers 
by a plentiful dilution with common water to hinder his lettuces from run¬ 
ning to seed, which otherwise they would do. A practical hint derived from 
one not conscious of theory. 
Dews advance vegetation from this source. 
Electricity augments the natural evaporation of fluids, and especially of 
those fluids which are most subject to evaporation of themselves; and it has 
also a great effect on fluids, when the vessels containing them are non- 
electrics. If a humid body, a sponge for instance, be placed upon a conductor 
positively electrified, the evaporation will go on much more rapidly, and it 
will be much sooner dry, than a similar body differently circumstanced. 
When water is passing out of small tubes in a continued stream, if these 
be electrified, the whole escapes in fine sprays, and evaporates in the form of 
dew. 
Signor Yolta has observed, that water in a state of evaporation, as when 
thrown upon hot coals, produces always negative electricity. 
There are many operations of Nature constantly carrying on, which 
escape the ordinary observations of mankind, but when known excite the 
highest sense of astonishment. 
The evaporation of water, and the fall of dew is of this nature. 
Who could have conjectured, says the learned Bishop of Landaff,* 
that an acre of ground, even after having been parched by the heat of the 
sun in summer, dispersed into the air above 1600 gallons of water in the space 
of twelve of the hottest hours of the day? No vapour is seen to ascend, and 
we little suppose that in the hottest part of the day, more usually does ascend 
than in any other. The experiment from which I draw this conclusion, is 
so easy to be made, that every one may satisfy himself of the truth of it. 
FIRST EXPERIMENT. 
On the 2d of June, 1J 79 , when the sun shone bright and hot, I put a large 
drinking glass, with its mouth downwards, upon a grass-plat which was 
mown close; there had been no ram for above a month, and the grass was 
* Vide Chemical Essays, vol. iii. 
2 Z 
