“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.