160 
electric fire, and vapours raised from them float in the air, forming clouds, which 
retain their electricity till they meet with other bodies, either destitute of it. 
been well soaked with rain, provided the heat be the same. I did not happen to mark the heat of the 
ground when I made the fore-mentioned experiments; the two following are more circumstantial: the 
ground had been wetted the day before I made them by a thunder shower, the heat of the earth, at 
the time of making them, estimated by a thermometer laid on the grass, was 96 degrees; one experi¬ 
ment gave 1973 gallons from an acre in 12 hours, the other gave 1905. Another experiment, made 
when there had been no rain for a week, and the heat of the earth was no degrees, gave after the 
rate of 2800 gallons from an acre in 12 hours; the earth was hotter than the air, as it was exposed to 
the reflexion of the sun’s rays from a brick wall. 
To shew how much electricity has to do with this phenomenon, the learned bishop made after¬ 
wards the following experiments. Upon the same grass-plat, and contiguous to the glass used in these 
experiments, I placed a silver cup, with its mouth downwards, of a shape similar to that of the glass, 
and nearly of the same dimensions; but I could never observe that its inside had collected the least 
particle of vapour, though I frequently let it stand on the grass for half an hour, or more. 
By means of a little bees-wax, I fastened an half crown very near, but not quite contiguous, to 
the side of the glass, and setting the glass, with its mouth downwards, on the grass, it presently 
became covered with vapour, except that part of it which was near to the half-crown. Not only the 
half-crown itself w as free from vapour, but it had hindered any from settling on the glass which was 
near it, for there was a little ring of glass surrounding the half-crown to the distance of three quarters 
of an inch which was quite dry, as well as that part of the glass which was immediately under the 
half-crown; it seemed as if the silver had repelled the water to that distance. A large red wafer as 
containing lead had the same effect as the half-crown; it was neither wetted itself, nor was the ring 
of glass contiguous to it wetted. A circle of white paper produced the same effect, so did several other 
substances, which it would be tedious to enumerate. 
These phenomena respecting the different dispositions of different bodies to attract the rising 
vapour, are similar to what others have noticed concerning the falling of dew, and are, probably, 
to be explained upon the same principles, whatever they may be. Muschenbroek placed on the leaden 
terrace of the Observatory at Utretcht, vessels of glass, china, varnished wood, polished brass, and 
pewter: he found that in the course of a night the glass, china, and varnished wood, had collected a 
great abundance of dew, but that not a drop had fallen on any of the polished metals. M. Du Faye 
exposed to the air, when the dew was falling, two large funnels, one made of glass, the other of 
polished pewter; the necks of the funnels being inserted into vessels proper to retain any moisture 
which might be collected by them; he sometimes found in the morning that the vessel under the glass 
funnel contained an ounce of more water, but he never observed so much as a drop in the other. 
Ihese experiments are found to correspond with those of the Abbe Nollet, who found, that evapora¬ 
tion of ail fluids was accelerated by electricity, hence their quick and sudden ascension in capillary vessels, 
fiom tnis power, and hence their quicker diffusion in the air, when contained in metallic vessels than 
in those fabricated of glass. 
Thiio it is that evaporation is the product of both heat and electricity, and water rises in 
the air, flying on the wings of electricity, till it arrives at those cold and rare regions, which is 
a conductor of electricity (for air approaching to a vacuum is found to be a conductor). To this 
thin,. 01 rare aii, electncity has a greater affinity than to water, the water becomes in part forsaken, 
and its particles attracting each othei, lose their transparency, and clouds are generated, which drop, 
accoidin^ to the respective densities of the stratas of air. If still more electricity be withdrawn 
then lain is pioduced. 01 that haziness which is sometimes seen to proceed on a sudden, over¬ 
casting, what appeared but a few minutes before, the brightness of an universal azure, which can be 
accounted for upon no other principle. That evaporation, clouds and rain are thus produced, may be ele- 
^ant.y 1 unrated by hanging a pair of small pith balls, by flaxen threads, in a receiver, and elec- 
tri ymg them positively: if the receiver be placed on the air-pump, and exhausted, the balls will close; 
? Cn Va ?° m becomes forsaken, and descends in the receiver, the balls open with negative 
electricity shewing that the rarefied air absorbed the electricity, and left the water to which it 
was united; thus completely forsaken, it falls within the receiver, an actual shower of rain. 
