157 
hail-stones and drops of rain are very small/* there being but a small space 
through which they can fall. 
Clouds of snow differ in nothing from clouds of rain, but in the circum¬ 
stance of the cold which freezes them.^ 
Low and thick fogs (especially when as they rise the air above them is 
free from moisture) carry up to the exploring wire an electricity which will 
give small sparks repeatedly, and produce a divergence of the balls J from 
* Clouds consist of very small globules, which are repelled from each other by the power of elec¬ 
tricity, and when these, from a deficiency of this fluid, assemble together by the natural adhesive 
attraction possessed by homogeneous bodies, it is then that the shower descends, as these are no longer 
buoyant, and still losing the elastic influence from the earth being in a negative state with respect to the 
air, the drops increase and assume a decided form. This is beautifully illustrated by hanging a small 
metallic vessel containing water on the conductor of an electrical apparatus, with a capillary syphon 
affixed to it. The water from the syphon falls in drops: but when electrified, these divide into num¬ 
berless smaller ones, so as to resemble what is called a Scotch mist, i. e. the rain on the tops of moun¬ 
tains, or those November mists when the equilibrium of the electric fluid is on the earth, and in the 
heavens nearly equipoised. 
f This phenomenon is often seen in crowded assembly-rooms at Petersburgh. When the cold air 
is let in from the top of the room by a contrivance on purpose for ameliorating the air, the floating 
vapour will be suddenly frozen, and attach together, and fall down in the form of thin flakes of snow. 
That snow is composed of a congeries of small spicula, is proved from the following pleasing experiment. 
Take a tall phial of the nitrous acid, warm it, add to it the filings of silver by degrees, which will dis¬ 
solve. The phial being placed in a cold window, as it cools, the silver particles will shoot into crys¬ 
tals; several of these uniting will form a flake, and these precipitating from their increased weight, 
will fall to the bottom of the phial, as silver flakes, and one flake lie upon another, like those of snow. 
The lightness of snow, although in fact solid ice, is merely owing to the extent of surface, as the 
silver in the above experiment, or as gold can be so extended in surface, as to ride upon the least 
breath of air. Its whiteness is owing to the smallness and disjunction of the spicula forming its com¬ 
position, for ice when pounded will appear equally white. Eor further particulars respecting snow, 
vide Section xiii, page 70* 
+ Balls of pith insulated and suspended shew the quantity, or power of the electric fluid. Thus if 
suspended in a fog or mist they separate with positive electricity. 
The terms positive and negative, as applied to electricity, are thus explained by Dr. Franklin. 
“ Positive electricity is when there is an accumulation of the electric fluid, or too great a quantity in 
any body, and negative when there is a deficiency.” 
When the remarkable phenomenon of the charged phial was discovered by Muschenbroek at Ley¬ 
den, no plausible theory was advanced for its explanation previous to Dr. Franklin. From some expe¬ 
riments he was induced to suppose that electricity was a single elementary fluid, which he termed 
electrical fire; and that its phsenomena depended upon the different proportions in which it is formed; 
that this fire was equally diffused throughout all bodies, and when, upon any disturbance, there was 
more than the natural quantity accumulated, this excess he expressed by the term positive; and when 
there was any deficiency, such was implied by the term negative. This philosopher supposes twenty 
particles of electricity on the inside, and the same quantity on the outside; so that when the quantity 
withinside was doubled, the whole of the outside was expelled. Glass, according to Dr. Franklin, is 
not permeable to electricity. These two electricities have been since denominated the vitreous and 
resinous. In the year 1733, Mons. Du Faye, intendant of the French King’s gardens, and member 
of the Academy of Sciences at Paris, discovered, as he thought, two opposite and distinct species 
of electricity, which he termed the vitreous and resinous. “ Chance,” says this philosopher, has 
“ thrown in my way an universal principle, which casts a new light upon the subject of electricity. 
2 R 
