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ther cloud succeeds, it electrifies again the wire, though less than before. 
Sky-rockets sent through such thick, low, and continued fogs, often afford 
signs of electricity. 
Dr. Franklin s theory is as follows. The electric fluid, says this inge¬ 
nious philosopher, is strongly attracted by water; and by destroying the 
cohesion between its particles, and repelling them from each other, it becomes 
a powerful agent in evaporation.* * The waters of the ocean abound in this 
too rare or thin to form much resistance to its passage, and then we see lightning without hearing thunder. 
An humble imitation of those effects may be produced by the two circular boards, Fig. 26, about 
two feet in diameter, their edges rounded, and the whole covered with tin-foil. Let one be suspended 
from the ceiling by clean silken cords; and the other sustained on glass feet, parallel to the other; but 
so as to be brought nearer or farther from another. If the upper board be connected with the con¬ 
ductor, and the lower with the earth, and separated about two inches distant, and electrified; one 
hand touching the lower, and the other the upper, a shock will be received as far from the Leyden 
bottle; for, as has been shewn, it is but a plate of air that is charged instead of a plate of glass; 
the upper board being in a positive, and the under in a negative, state: the shock being in proportion 
to the quantity of electricity, and the ease with which it can escape from the positive side of the 
electric. The two plates strongly attract each other, and would come together, if not kept asunder by 
force: sparks flying between them will frequently destroy the electricity of each. If the under surface 
of the upper plate be covered with gilt leather, and a smooth shilling be laid on the lower plate, beau¬ 
tiful ramifications will fly about the leather, and dart to the shilling, when electrified. In this expe¬ 
riment the upper plate naturally represents a positive cloud, and the under one the earth, with the 
manner in which lightning darts from the clouds to the earth; and if a Leyden phial be connected with 
the conductor, the flash and report will be still the greater. Vide Walker’s Philosophy. 
* Those who have not been accustomed to contemplate the occurrences of natural events will be 
astonished to be informed, that an acre of ground, even after having been parched by the heat of the 
sun in summer, disperses into the air above one thousand six hundred gallons of water, in the space of 
twelve hours. The experiment from which this conclusion is drawn is as follows. On the 2d of June, 
1779 > when the sun shone bright and hot, I put, says the learned bishop of LandafF, a large drinking 
glass, with its mouth downwards, upon a grass-plat which was mown close; there had been no rain, 
for above a month, and the grass was become brown; in less than two minutes the inside of the glass 
was clouded with a vapour, and in half an hour drops of water began to trickle down its inside, in 
various places. This experiment was repeated several times with the same success. That I might 
accurately estimate the quantity, thus raised, in any certain portion of time, I measured the area of 
the mouth of the glass, and found it to be 20 square inches: there are 1296 square inches in a square 
yard, and 4 840 square yards in a statute acre ; hence, if we can find the means of measuring the quan¬ 
tity of vapour raised from 20 square inches of earth, suppose in one quarter of an hour, it will be an 
easy matter to calculate the quantity which would be raised with the same degree of heat, from an 
acre in 12 hours. The method I took to measure the quantity of vapour, was not perhaps the most 
accurate which might be thought of, but it was simple and easy to be practised: when the glass had 
stood on the grass-plat one quarter of an hour, and had collected a quantity of vapour, I wiped its 
inside with a piece of muslin, the weight of which had been previously taken; as soon as the glass 
was wiped dry, the muslin was weighed again, its increase of weight shewed the quantity of vapour 
which had been collected. The medium increase of weight, from several experiments made on the 
same day, between 12 and 3 o’clock, was six grains collected in one quarter of an hour, from 20 square 
inches of earth. If the reader takes the trouble to make the calculation, he will find that above lOoo 
gallons, reckoning 8 pints to a gallon, and estimating the weight of a pint of water at one pound 
avoirdupois, or 7000 grains troy weight, would be raised, at the rate here mentioned, from an acre of 
ground in 24 hours. 
It may easily be conceived, that the quantity thus elevated will be greater when the ground has 
