A Treatise on Electricity / Wherein its various phænomena are accounted for, and the cause of the attraction and gravitation of solids, assigned. To which is added, a short account, how the electrical effluvia act upon the animal frame, and in what disorders the same may probably be applied with success, and in what not.

by Francis Penrose

To prove this, Mr. Freke has brought, two very simple, common, but good experiments—First, if you slide a wax thread, or small rope, through your fingers, it will burn them; so likewise fire is produced, by rubbing two hard bodies together, or two sticks; or, as is very often the case, a cart or coach wheel will take fire, for want of grease.

Another no small proof of this, is what Mr. Freke has mentioned, viz. that in the year 1703, in the night of the great hurricane and high wind, in the strongest part of the tempest, great quantities of fire were seen passing swiftly over the hills in the neighbourhood of Warham in Dorsetshire. The cause of which fire seems very easily accounted for, according to the above theory, which might otherwise perhaps, elude the searches of our greatest philosophers: for in this phænomenon it is plain, that the attrition of the particles of the air was so great by the motion of the wind, as to produce fire or light. Mr. Freke has some other observations, which much strengthen the above theory, viz. that in tempestuous weather, at sea, great flakes of fire are frequently seen passing, not only in the air, but on the water. The like is also observed, in the night time, when the surface of the water is disturbed with the feathering of oars, or by a vessel or boat passing swiftly through it. This light or fire in storms is no new observation; for Mr. Boyle says, it is common in storms for the fire called Helena, Castor, and Pollux, to hover about the masts of ships. And, indeed,

To shew that fire or heat are produced in any place, or thing, where there is a sufficient motion, seems not to be very difficult; for water is the opposite to fire; and yet, by mixing water and spirit of wine suddenly together, a heat ensues; and this will happen if they have been separated ever so often; but this heat vanishes again after they are mixed, or as soon as the motion of their parts ceases. The like will happen by mixing salt of tartar and water. This phænomenon seems to proceed from the disposition and texture of the salt; whose pores are made of such a proper size, that, on receiving the water by the pressure of the atmosphere into them, the texture of the salt may be thereby broken, and its parts put into motion; which motion causes an attrition of the air, and so produces a sensible heat.

Boerhaave has another observation, which seems to prove to a demonstration, that fire or heat is caused by an attrition of the air; which observation I shall give in his own words. “A cannon ball, shot in the winter time, will fly 600 feet in a minute through the cold air, which makes a greater resistance than any wind, the most rapid of which only moves 22 1/2 feet; hence it appears how much friction the ball must have undergone in its passage, which by the way did not proceed in a right line, but by its whirling motion continually describes a cycloid with every point of its body. When it falls, it is found quite hot; notwithstanding in its whole passage, it had continually met with cold air. This heat could not have arisen from the flaming gunpowder, whereby it was exploded, since it only remained in that flame, an incredible small space of time, in which it is by no means credible so solid a body should have acquired such a heat; which is much more naturally accounted for from the great attrition of the ball, driven with such a velocity through the air, and repelled by a wind, which is above 27 times swifter than the strongest wind hitherto observed.” Boerhaave’s Chym. by Shaw, Vol. 1. pag. 244.

I shall mention one more experiment from Mr. Boyle, which proves that air is not only convertible into light; but that it may afterwards be forced through glass, and thereby the same vacuum be made that is by an air pump. “Liquid phosphorus being put into a vial, when it was disposed to shine in the dark, the cavity of the vial above the liquor seemed to be full of whitish fumes, though at other times transparent. The vial, when close stopped, was not luminous in the dark, but the light or flame appeared as soon as it was exposed to the air, and the vial was unstopped; and that the occasion and propagation of this flame depended on the contact of the air, appeared, since agitation would not kindle it, but when the bottle was unstopped, the kindled flame would gradually be propagated downwards; the flame always appeared most vivid the nearer the air, and when it was extinguished, it first disappeared in the bottom, and then expired at the top. When the Vial was unstopped for some time, when it was stopped again, the air that had leisurely insinuated itself would cherish the flame for an hour or two. It was observable, that when the air had been long pent up with this shining liquor, its resistance would be so weakened, that when the vial was unstopped, the external air would presently rush in with violence, from whence appears the interest of the air in propagating the shining of this liquor. The agitation before the vial was unstopped would not kindle the light; yet when it was opened, it would be increased by it, and even when it was in its dull state, if I poured a little of it upon my hand, and rubbed it with my finger, it would presently become vivid, and emit store of luminous rays, as well as fumes very offensive to the nostrils; and when I ceased to rub, and the luminous quality was lost, it would be renewed again by a repeated attrition; but in a little time its lucid virtue would decay,” Boulton’s Epitome of Boyle’s works, vol. 2. pag. 246. From these experiments it may be observed, that this liquid phosphorus could not be made to emit light, without a communication with the air, not even by the utmost agitation; though when it had a free communication with the air, a small agitation greatly increased the quantity and strength of the light; that, whenever the air was admitted to join it, a violent intestine motion came on, by which motion or attrition, light was not only produced, but also a great deal of the liquid was carried off by it; which might be perceived either by the sight, or smell. And when the vial had been long without a cork, by which means it was filled to the utmost with air, the light would continue a considerable time after the vial was stopped. We likewise find, that, after the vial has been stopped some time, and the liquor has acted upon the air as much as it possibly can, there is not only a less quantity of gross air than there was when the vial was first stopped, but that there is the same vacuum as is made by the air pump; for as soon as ever it is unstopped, the air presseth in with violence, the fluid above the phosphorus (within the vial) being of a more subtle nature than the air without.

This experiment seems sufficiently to prove, that air and light are of the same essence or substance; for we are certain that gross air entered the vial, and, when it was first stopped, the quantity of gross air was of an uniformity with the air without the vial; but at its being opened, we are assured, there was a less quantity than when it was first stopped; for the air without presseth in with the same violence it does into the exhausted receiver of an air-pump; by which we may be assured, that some parts of the air have passed the vial in form of light; and, as the pores of the glass are not big enough to admit gross air to return, the consequence must be, that there is a less quantity of gross air in the vial at the opening, than there was, when it was first stopped.

Fire and light are easily proved to be dispersed through the whole air, from the immediate action of speculums; and that air itself is of the same substance with fire seems very plain; for as fire cannot subsist without air, (and in proportion to the quantity of air forced into the fire, in such proportion will be the force of the fire;) so, neither can fire act but on the outside of bodies next the air; for even the most inflammable bodies can only catch fire on their outermost surface contiguous to the air; and fire in action, if immerged in a body of the most inflammable matter, so as to leave no lighted part above such surface in the air, will be so far from kindling the inflammable body, that itself will be extinguished. Thus “if a flaming brimstone match be plunged into the highest rectified spirit of wine, the spirit of wine will extinguish it as intirely, as if dipped in cold water; it will also extinguish a live burning sparkling coal; but in the former experiment, if the least bit of the burning match remains above the spirit of wine, it will then catch fire, and the flame will presently spread over the whole surface.” This is an experiment of the great Boerhaave, in the first vol. of his chymistry, by Shaw, pag. 316.

All these experiments, I think, prove to a certainty, that air is convertible into light. I shall now bring one experiment, from Boerhaave, Vol. 1. p. 998. which proves, that fire or light may be changed into air.