This fire gives elasticity: and elasticity or vibration is the mother of electricity. We don't so much wonder at phosphorus arising from animal substances; for this fire is in water, and betrays itself to our senses, in salt water. Many a time when I have passed the Lincolnshire washes, in the night time; the horse has seem'd to tread in liquid flames. The same appearance is oft at the keel of a ship. Fire exists in water, says Pliny, as well as in human bodies. nat. hist. II. 107. Loaf sugar beaten in the dark is luminous. Many vegetables, as indian cane, and rotten wood the like, as Bartholin largely recites, de luce hominum c. 4. All electric bodies have this privilege: that is, they more easily discover it. Amber, gum lac, naptha, bitumens, some precious stones. My old friend Mr. Stephen Gray the father and great propagator of electricity, show'd me experiments therein, in the year 1705, then at Corpus Christi college in Cambridge. Afterward in the year 1719, he show'd by experiments before the Royal Society, that paper, ribbands, silk, sattin, cloth, shavings, linen, goldbeaters skin, and in short, almost all kind of substances discover electrical sparks of fire in the dark: especially when well warm'd before the fire, or in a cold, dry, nitrous air, and in a room where there is no company. This same quality is found in vacuo, as Dr. Desaguliers show'd before the Royal Society, march 31, 1720. He took an exhausted glass globe, and caused it to be turn'd round violently, in an engine: by rubbing the hand upon it, it was illuminated within side, with purple streams. This gave foreigners the idea of using a glass globe, in electrical experiments.
The operation of the ethereal fire is various, nay, infinite, according to its quantity, and degree of incitement, progress, hindrance, or furtherance. One degree keeps water fluid, says the learned bishop of Cloyne: another turns it into elastic air, and air itself seems nothing else, but vapors, and exhalations render'd elastic, by this fire.
This fame fire permeates, and dwells in all bodies; even diamond, flint, and steel. Its particles attract with the greatest force, when approximated. Again, when united, they fly asunder, with the greatest force, and celerity; it resists nothing quiescent, but when put into motion, it disdains all resistance. All this is according to the laws prescrib'd by the sovereign architect. This is the life, and soul of action, and reaction, in the universe. Thus has the great author provided against the native sluggishness of matter! light, or fire in animals, is what we call the animal spirits; and is the author of life, and motion. But we know not the immediate mode of muscular motion; any more than how, in inanimate matter, it causes the vibrations of an earthquake.
Of this fire, the excellent Manilius thus writes, who liv'd in the time of Augustus.
Astronom. I.
Sunt autem cunctis permisti partibus ignes;
Qui gravidas habitant fabricantes fulmina nubes:
Et penetrant terras, Ætnamq; imitantur Olympo:
Et calidas reddunt ipsis in fontibus undas.
Ac silice in duro, viridiq; in cortice sedem
Inveniunt; cum silva sibi collisa crematur.
Ignibus usq; adeo natura est omnis abundans!
Which may thus be english'd.
Fire universal nature traverses.
It makes the thunderbolt in tumid clouds:
In dire Vulcano's penetrates the earth:
And sends the boiling water from its springs.
In hardest flint, and softest wood it dwells:
Which by collision shows itself in flame.
With fire so pregnant is all nature found!
13ly, The great question then with us, is how the surface of the earth is put into that vibratory and electric state, by heat and driness? we must needs acquit the internal of the earth from the charge of these superficial concussions. How then is the ethereal fire crouded together, or excited, so as to cause them; seeing in our ordinary electrical experiments, we make use of friction?
But that friction alone does not excite electricity, we know from the obvious experiment of flint and steel, where the suddenness of the stroke, and hardness of the matter does it. Another method of exciting it, is the letting off a number of great guns, which so crouds the ethereal fire together, as to electrify glass windows; observ'd by my friend the reverend Dr. Stephen Hales. The aurora borealis, australis, all kind of coruscations, meteors, lightning, thunder, fire-balls are the effects, and may reciprocally be the cause of electricity; but how in particular we know not. Come we to the animal world, we must needs assert, that all motion voluntary, involuntary, generation, even life itself: all the operations of the vegetable kingdom, and an infinity more of nature's works, are owing to the activity of this electric fire, the very soul of the material world. And in my opinion, 'tis this alone, that solves the famous question, so much agitated with the writers in medicine, about the heat of the blood. How these, how earthquakes are begun, propagated, we are yet to seek.