Francis Penrose

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ON
ELECTRICITY.

The many surprising effects of electricity, and the great cures performed by it, one would imagine, should awaken the attention of all philosophers and physicians; but as these cures have been effected by random experiments, every body has admired, but no body seems to have considered how, or by what means, they were performed. Whence

Notwithstanding all these surprising phÆnomena, from which many have entertained hopes of a great addition to the healing art; yet not one tolerable account has been given, how, or from what cause, these phÆnomena proceeded; except what has been done by Mr. Freke, surgeon to Bartholomew hospital; whose admirable piece shews the great penetration of its worthy author, with whom I shall join in thinking “it may possibly be the beginning of much good.”

One would think, this silence, on so interesting a subject, in this enlightened age, can proceed from nothing but a prejudice in favour of wrong principles of philosophy: That this is certainly the taste of the present age, M. Freke seems very well convinced; for, at the end of his pamphlet, he takes notice of a show-man, who, “having published some experiments in electricity, and hearing that Mr. Freke’s piece was publishing, own’d, he was much affrightened, because of the hard fate, as he said, of his booksellers; but, before he had read two pages, he likewise owned he had recovered his spirits, when he found Mr. Freke pretended to think for himself, and did not let Sr. Isaac Newton think for him.”

Now, if all persons would take the same freedom of thinking for themselves, as Mr. Freke has done, I doubt not but we should soon be as much ashamed of mentioning the attraction of gravitation, and the attraction of cohesion &c. as we now are of the occult qualities of the ancient philosophers; and should perhaps, then agree with him, when, speaking of electricity, he says, that “it is a subject which can, with more nobleness and dignity, employ the mind of man, than any he can think of, relating to the sublunary part of the world. For by it you may be acquainted with the immediate officer of God Almighty, which he seems to send to all things living: Nay, this power, (according to his conception,) seems to be the cause, under Him, both of life and death. And when it may be more fully understood, it may afford us means, whereby we may be better enabled to reason more intelligibly, than now we can, concerning various operations in nature.” Therefore,

In the following essay, I shall endeavour to shew,

I. How, and from whence, this electrical fire and force are produced; in doing of which I shall make some observations, in order to shew that we may form a more exact idea of most of the great operations of that complete machine, the universe, from electrical experiments, than can be attained by any other means: I shall also produce some experiments which demonstrate, that the terraqueous globe has no attraction; nor a solid body, falling towards the earth, any gravitation; after which, I shall bring other experiments to prove what is the cause of solidity, and by what means bodies gravitate towards the earth.

II. How this electrical fire and force act upon the animal frame, and in what disorders they are likely to be of benefit, and in what not.

I. We are certain, that this electrical fire is produced, either from the glass globe, or the air that surrounds it. As to the glass globe, Mr. Freke has fully proved it cannot proceed from that; “Because nothing, we know of, can send out of it a quantity of matter, but there must be less of that matter remaining, after it has been so discharged; whereas it cannot be shewn, but that the glass globe, after ever so many times using, remains as fit for the same use, as at first.” From hence we assert, that this fire must proceed from the surrounding air being acted upon by the glass globe; and our inquiry must be, how, and by what means, fire is produced by the glass globe being made to act upon the air by which inquiry we shall find, that air, light, and fire are of the same substance, or essence; only differently modified, and appointed for performing different actions: that air (by being divided or broke to pieces) produces light; and, if that action is still encreased, it produces fire. Now as the greatest friction or attrition are necessary to produce fire, so fire, when it is once produced, having received the greatest force, of consequence acts with the greatest force; and light, with a less; so, wherever there is the greatest quantity of these small particles of air, (which we call by the name of fire) in proportion to what we call gross air, there the action must be the greatest; by which means the said fire or light will expand itself, ’till, by mixing with what we call gross air, it becomes of an uniformity with it. Now therefore, as experiments are the sure way either of proving or disproving any hypothesis; so, to illustrate this, I shall produce some experiments both from Mr. Freke, and other authors of unblemished credit, which prove that air is convertible into light and fire, and also that light and fire are convertible back again into air; and likewise, as some parts of the air are present in all places and things, that therefore, whenever a violent action either of solids or fluids is brought on, there light, fire, or heat, are produced.

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.

“If a spherical glass vial be kept in a glass-house furnace, till ready to melt, and then be hermetically sealed in that heat, and suffered to cool; if now, it be held inverted, under cold water, and the end of the neck be carefully broken off, the water will be violently forced into it, and fill the glass, but so as to leave a bubble of true elastic air at the bottom.”

The above experiments prove, that, whenever air is sufficiently divided or broken to pieces, light is produced; so that the light or heat in electricity, is no other than, we find, may be produced several other ways. For the air being violently rubbed or ground to pieces between your hand and the glass globe, whirled briskly about, the air between your hand and the globe is ground so small as to be in the form of light, which is expanded or sent off from the glass globe in the same manner as light from a candle, or other luminous body; which emission is continually supplied by the common air pressing in between the rays of light, emitted from the glass ball. That this is the method, by which it acts, seems very clear: for you may not only hear the hissing noise of the air pressing towards the globe, but also plainly feel the air with your hand, near the globe or tube.

The chief reason (and what has been our great misfortune) that we have not been able to discover the cause of electricity, seems to be the leaving that philosophy, which has been revealed to us, and putting in its stead theories of our own invention. For, if we had considered (from the revealed account that is given us of the formation of light) the method of its first production, we should not be at such a loss to account for that light in electricity, as we hitherto seem to have been; for we are there told, that the heavens, or airs, were created in a state of darkness, or inactivity; and that the first thing God did, was to cause a motion, or wind amongst the airs; which motion was to continue, and encrease, till it produced light; and, after this light was produced, God called it Day, or as it is expressed in the original, tumultuousness; it being produced from the impetuous or violent motion of the airs: and the darkness he called night, or, as it is likewise expressed, the time when this languishes or decays; for the congealing or thickning of the air, by which darkness is produced, is in proportion as the force of the light abates.

By all which, I think, we may be assured, that the light, and all the phÆnomena produced in electricity, are caused by a violent friction or grinding of the grains of air between the glass globe and the hand.

To illustrate and prove, that this is the method by which the electrical light is produced, I shall bring some experiments, from Mr. Hauksbee, which, I imagine, will make it indisputable. In his first and second experiments, he shews us, that by dropping mercury on a glass in an exhausted receiver, the action of the mercury on that subtil fluid gives the mercury the appearance of fire; but observes, that in all these experiments on mercury, no light is to be obtained without motion, and that the same motion which produced this light in vacuo, did not produce it, when given to mercurial globules in open air. This experiment shews us, that there was a larger quantity of light in the exhausted receiver than when it was filled with common air; nay farther, that the subtil fluid contained in the exhausted receiver, was light; but, for want of motion, was not perceptible by our senses; but by so small a motion as that of the descending mercury, it was pushed forward in the same manner, as light from a candle, or other luminous bodies. We also find, that the same experiments performed in an unexhausted receiver, would not produce the phÆnomenon of light; which one might easily suppose to be the case. For in the exhausted receiver, any the least motion, that is sufficient to push this subtil fluid (light) from one place to another must give us the perception of light; but in the unexhausted receiver the motion or friction must be great enough, not only to push the air from place to place, but also to break it so small, as to be in form of light: which he shews us by his third, fourth, and fifth experiments to be the case; for by these experiments he produced light in an unexhausted receiver; but then the motion or agitation was required to be much greater than that which produced light in vacuo. The difference of these two lights was very considerable, and consisted particularly in this, that the luminous particles are distinct and separate in the experiment performed in the open air; and united and blended into one continued body of light, in the other experiments in vacuo; which difference proves to a demonstration, that the exhausted receiver was full of nothing but light; for, on shaking the mercury therein, the whole body of the receiver seemed to be one continued body of light; but on shaking the mercury with ever so great a violence in the common air, it seemed full only of little, bright, twinkling sparks; and not one continued body, as in vacuo. For, as the appearance of light is produced in the common air, by the friction of the mercury against the glass receiver, breaking or grinding the air to pieces (which small particles put on the form of light) so, when the common air presses in between these small particles, the appearance must be, and cannot be otherwise than is shewn by these experiments.

These many and various experiments abundantly prove, that light is produced as above described; and not, as the generality of people have imagined (from that mistaken notion of action being performed by solids and not by fluids) that this electrical light proceeded from the glass globe, emitting, what they call, electrical effluvia, which has been shewn before to be impossible; because if any quantity of matter sends off part of its own body, there must be less of that body remaining, than before the above matter was sent off, which we find is not the case of the glass globe; and to prove that it does not, I shall bring one experiment more from Mr. Hauksbee which will put it beyond doubt.

Pag. 27. he shews us, that by a violent attrition of woollen against woollen in vacuo, he produced light, as well as from any hard or electrical body; but not so vivid, nor in so large a quantity. Now, as woollen is reckoned by all to be a non-electrical body, it shews us that the light must proceed from the attrition of the air, and not from the electrical body, as has been falsely imagined.

As light may be produced by other methods than have been yet described, as from rotten wood, fish, meat &c. I shall endeavour to give an account, how, and in what manner, that light is produced. Mr. Boyle (in vol. 2. p. 233. of the epitome by Boulton) tells us, that by putting rotten wood, fish, flesh &c. in the receiver of an air-pump, and then extracting the gross air, they all, in a little time, lost their shining or luminous quality; but, upon a re-admission of air, this luminous quality returned. From which we may learn, that the air is essentially necessary to continue this light; and, of consequence, that this light is produced by the action and re-action of the air on the body, which cause an intestine motion of its parts; and thereby the emission of the said light; for when any thing begins to ferment and putrify (which cannot be performed in any place, but where the gross air is present) the intestine motion of its parts is thereby increased; which motion acting upon the air pressed into it, the air is thereby ground very small, and by the continual pressure of the atmosphere is sent out so small, as to be in form of light.—In the common fermentation of liquids, when it rises to any height, those particles of light being stopped, and entangled by the watry parts of the fermenting mass, thereby produce heat; and some mixtures will produce light, heat and flame on fermentation; as steel, water, and sulphur.

By these experiments we have a clear idea of the means and method by which fermentation is performed, which operation has been hitherto unintelligible. From hence we may likewise see the reason why, in an air either too hot or too cold, fermentation cannot be performed; for in an air too cold, the pressure is too great, and also the grains of air too large to enter and divide the thing to be fermented; by which means the motion of its parts requisite to fermentation is prevented; but in air that is too hot, there must be just the contrary effect, for there the parts of the thing to be fermented are so far expanded, and the air so rarified, as to pass through the body with little or no obstruction, and of consequence to produce little or no intestine motion of its parts; and that there is in fermentations an intestine motion of the parts of a fermenting liquid, is easily discernible by the naked eye. This also gives us the reason, why the glow-worm shines only in the summer months, when the air is greatly rarified, or divided, and then requires but a small motion to give it the form of light.

The light proceeding from diamonds &c. seems to be easily accounted for from the motion of the airs; that there is a perpetual motion of the airs, may be proved by the following experiment. In a still place, suppose a close darkened room, illuminated only by one small hole in the window shutter; where, if a person at rest views the enlightened current of air sideways, as it extends along the room, he will perceive a surprising motion of the dusty atoms therein, perpetually rolling and tossing about with great rapidity. This motion must be very considerable, as it is perpetual, and pushed on with the power of gravity in the air equal to a column of water 33 feet high. By this action on diamonds, whose pores are very small, and the bodies themselves of such a make and hardness, as that, when the air is pressed on them with so great a force as that of the incumbent atmosphere, the air is broke exceedingly small, and, by the continuance of the pressure, is sent off from the body in form of light. We likewise find from experiments, that where diamonds, or other bodies of that kind, have not their outward parts of a proper make, or their substance of a sufficient hardness or closeness of parts, to emit light with no greater force, than the pressure of the atmosphere only, then this deficiency may be supplied by rubbing; by which means the air is ground to pieces, and emitted in form of light, as is shewn in all electrical experiments.

One great property of light, or, as it is commonly called the electrical effluvia, is (as Mr. Hauksbee has proved from many experiments,) that it passes through glass, as water does through a sieve, or as if no body of matter interposed. This light of itself, when pure, or simple, hurts or destroys no material bodies; but when pushed on by the following air with great violence, and meeting with a great resistance from an impeding body, the conflict is so great, that if the following air presses on with sufficient violence, it dissolves or destroys the solidity of any material body. As all bodies become solid according to the temperature of the surrounding air; some retaining their solidity in such a degree of heat, as metals of most kinds; whilst others require a particular degree of cold before they become solid, as water &c. which when froze is as much a solid as any thing else—this proves that the solidity of bodies depends on the temperature of the air, as will be more fully proved hereafter.

The glass globe, with the electrical experiments, seems to give a very clear idea in what manner the sun is supported, how this terraqueous globe and the rest of the planets are made to move, and continued in motion; and also, what is the cause of the attraction of the sun, earth, moon and the rest of the planets.

That the sun is the chief, material, ruling agent, is very clearly revealed; as are some of its chiefest actions on the planets and the rest of the universe. For, in the sun we find a power of melting, dividing and (with the assistance of the air) expanding and sending out the air, first in form of fire, and afterwards in that of light; which power seems to be so regulated, as to be able to reach the extremities of the universe, where it is congealed, condensed, and returned back again to the sun, to be again melted, divided, and sent out as before. This action seems to be represented by water in a still, for there the fire, forcing its way through the water contained in the still, carries off some of the watry particles with it; and when it has reached the head of the still, if it has no passage into the outward air, and the action of the fire is not great enough to break the still, it is by the coldness of the surrounding air (or as is commonly the case by the coldness of water placed thereon for that purpose) condensed and returned into the water contained in the body of the still, there to be rarified, expanded, and sent off in steam, as before.

We must suppose the streams of light to be always acting on one side of this terraqueous globe, and there dividing, expanding and rarifying the air; the consequence of which must be a kind of vacuum, which is immediately filled by the pressing in of the congealed air from the extremities; and as the earth is placed in this fluid of airs, we may as easily conceive that the air pressing in as above, must, with it, turn round the earth, in the same manner, and with as much ease, as water does a common mill-wheel, or the air a wind-mill. By these powers also the terraqueous globe is kept solid and entire; for, was this force once taken off, it would soon drop to atoms, notwithstanding the pretended attracting power of its materials.

To confirm what is here advanced, I shall bring an experiment (which Mr. Boyle has laid down as a paradox) which proves that this terraqueous globe has no attraction, nor any solid, falling towards it, any gravitation; but that all bodies are forced to it by the incumbent atmosphere, as much as water is forced up a pump by it (the atmosphere) which, till the time of the great Mr. Boyle, was imagined to be performed by, what they called, the suction of the pump. But this is no more than has often happened in philosophy, where when we cannot well account for any thing, we put the effect for the cause.

Mr. Boyle found that a solid body, as ponderous as any yet known, though near the top of the water it would sink by its own weight, yet if it be placed at a greater depth than twenty times its own thickness, it will not sink, if its descent be not assisted by the weight of the incumbent water. To prove this, he gives us a curious experiment, viz. by keeping off the pressure of the water, from the top of the sinking body, and sinking it to a proper depth, he found, that the most ponderous body would be buoyed up, and supported by the water only. See the 2d vol. of Boulton’s epitome, pag. 305. This experiment shews us beyond all contradiction, that the earth has no power of attraction, nor a descending body any power of gravitation; for if it had, the farther it was sunk in the water, the nearer it must be to the centre of the earth, and of consequence the attraction must be the greater; but this, we find, is contrary to experience; so that the whole power of descending is impressed upon it by the air, or by other bodies forced upon it by the incumbent air. This experiment alone is more than sufficient to destroy the fine theories of attraction and gravitation; it also shews us how, and by what means, two marble slabs, finely polished, are what they call attracted to each other, and require a great force to separate them; a force in proportion to the breadth of the slabs; but this has been shewn by other experiments to be nothing but the pressure of the air, or atmosphere; for put them into an air pump, and extract the gross air, and they will immediately separate from each other.

One reason, which seems to have led us into the mistake that the solidity, or firmness of bodies is not caused by the air, has been, that, for the generality, we consider the air, or atmosphere as pressing only downwards; for if we had considered that it presseth equally every way, as well as downwards, (as Boerhaave in his chym. by Shaw, vol. 1. p. 389. has shew by the following experiment) I believe we should not have overlooked that force, or have thought it insufficient for this operation. “Fill three glass vessels, the one of a cylindrical figure, the other conical, the third bellied with a cylindrical neck; let these be filled to the brim with fair water, and covered with a single piece of paper, so as to touch the surface of the water, and by pressing it down with the hand, prevent the external air insinuating between the paper and the water; if the glasses be now inverted, whilst the paper remains close with the palm of the hand, and the hand be afterwards gently withdrawn, the water will still remain in the glasses. The same holds true, though the glasses be held horizontal, or in any other position.” As the cause of the solidity or firmness of bodies is the pressure of the air or atmosphere, so likewise it must depend on the make and size of the pores of such bodies; for bodies whose pores are smallest, must be acted upon with a greater power than those whose pores are largest, or whose pores are so large as not only to admit light, but also common air into them. This Mr. Hauksbee proves by a curious experiment, for having placed two brass hemispheres, of 3 1/2 inches diameter, upon each other, and then extracting the gross air out of them by the air pump, and by these means taking off the resistance of the common air that was within the two brass hemispheres, he says, it required 140 pound weight to separate them; this experiment with that of the two marble slabs before mentioned, is a demonstration of the power that keeps solid bodies from falling to pieces. And even, if these slabs are not so perfectly smooth, yet the weting them with water, which prevents the gross air from entering, will produce the like effect. That solids expand themselves by heat or fire, is proved by heating an iron rod in the fire: in which case, it is always found to be bigger and longer when hot than cold; and it was the opinion of Boerhaave, that cold consolidates all those that are called firm bodies; that is, brings that part, which we call body in them, into a less compass than before, and thus unites the matter thereof more closely together: by which means the cohesion of the whole mass is usually increased; which makes what we call, strength and firmness in bodies.

Having shewn that solid bodies have no power either of attraction or gravitation, and that their firmness or solidity depends on the pressure of the atmosphere; I shall now endeavour to shew, from electrical experiments, how, and by what means they descend towards the earth.

What is called the attraction of the earth seems to be performed in the same manner as that of the glass globe in electricity; the explaining of which will give us a clear idea, by what means heavy bodies are forced towards the terraqueous globe. In accounting for this electrical attraction, Mr. Hauksbee seems to be very clear; for, says he, “if by the heat and rarefaction, consequent upon the attrition, the medium contiguous to the glass be made specifically lighter; then of course, to keep up the ballance, the remoter air, which is denser, must press in towards the tube, and so carry away (in the torrent) the little bodies lying in its way, thither also. The various irregularities in the excitation, or the emission and discharge of the electrical matter or light from the tube (which will be followed with proportional irregularities, in the motion and tendency of the denser air, towards the glass globe, by the hydrostatical laws) may be sufficient to account for the various uncertain motions of the little bodies carried towards the glass globe.” This account of Mr. Hauksbee’s being so very clear, it is a little surprising that he should allow the power of attraction to matter, as in some places he does; for this is no more than in other words, telling us, that the air round the ball is divided and rubbed or ground to pieces by the friction between the glass globe and your hand, and thereby made to expand itself; so the air pressing in to make up that deficiency, forces every thing towards the glass globe, that by its number of particles is not able to withstand the current of air, pressing towards the globe. So in like manner near the surface of the earth, the sun-beams being reflected by the terraqueous globe, must by these means be in a greater quantity near the surface of the earth, than at a distance from it; and so divide, expand and rarify the air near its surface, which rarified or divided air is forced off from the earth on all sides, by the pressing in of the air from above, which must of consequence drive every thing before it, towards the earth. By which we find, that the cause of bodies descending towards the earth, is not from any property either of the earth or of the descending bodies; but that these are forced towards that, by the surrounding air, in its said motion.

To prove that this is the method by which, in electricity, bodies are forced towards the glass globe, I shall bring an experiment or two from Mr. Hauksbee; and as these experiments prove to a certainty, that this is the manner of the attraction in electricity, it will give us little room to doubt, but that the attraction of the earth is performed in the same manner.

Mr. Hauksbee observed, that the electrical effluvia were not only perceiveable by sight; but also, if the hand was held near the tube, seemed to make such sort of strokes upon the skin, as a number of fine limber hairs pushing against it might be supposed to do: and in order to find whether the electrical attraction was regular and uniform, he made the following curious experiment, shewing that all bodies, not too heavy, are forced (or, as is commonly supposed, attracted) to a cylindrical glass, equally all round, if these bodies are, as they term it, within the sphere of its activity.

This experiment seemed to affect Mr. Hauksbee so much, that (speaking of electricity) he says, “it affords us a sort of representation of the great phÆnomena of the universe.” Page 53.