Chapter I: HAVE made several Trials in order to fire Gunpowder alone, which I

tried both warm and cold, whole and powder'd, but never could make it succeed; and this arises in part from its Vapours not being inflammable, and in part from its not being capable of being fir'd by Flame, unless the Sulphur in the Composition is nearly in the State of Accension. This we see by putting Gunpowder into a Spoon with rectified Spirit, which, when lighted, will not fire the Powder, 'till by the Heat of the Spoon from the burning Spirit, the Sulphur is almost melted. Likewise, if you hold Gunpowder ground very fine in a Spoon over a lighted Candle, or any other Flame, as soon as the Spoon is hot enough to melt the Sulphur, you see a blue Flame, and instantly the Powder flashes off. The same Effects are observ'd in the _Pulvis fulminans_, compos'd of Nitre, Sulphur, and fixed Alkaline Salt. Besides, when the Gunpowder is very dry and ground very fine, it (as you please to make the Experiment) is either attracted, or repell'd; so that in the first Case, the End of your Finger when electrified, shall be cover'd over with the Powder, though held at some Distance; and in the other, if you electrify the Powder, it will fly off at the Approach of any non-electrified Substance, and sometimes even without it. But I can at Pleasure fire Gunpowder, and even discharge a Musket, by the Power of Electricity, when the Gunpowder has been ground with a little Camphor or with a few Drops of some inflammable chemical Oil. This Oil somewhat moistens the Powder, and prevents its flying away; the Gunpowder then being warm'd in a Spoon, the electrical Flashes fire the inflammable Vapour, which fires the Gunpowder: But the Time between the Vapour firing the Powder is so short, that frequently they appear as the same and not successive Operations, wherein the Gunpowder itself seems fired by the Electricity; and indeed the first Time this Experiment succeeded, the Flash was so sudden and unexpected, that the Hand of my Assistant, who touch'd the Spoon with his Finger, was considerably scorch'd. So that there seems a fourth Ingredient necessary to make Gunpowder readily take Fire by Flame, and that such a one, as will heighten the Inflammability of the Sulphur. In common Cases the lighted Match or the little Portion of red hot Glass, which falls among the Powder, and is the Result of the Collision from the Flint and Steel, fires the Charcoal and Sulphur, and these the Nitre. But if to these three Ingredients you add a fourth, _viz._ a Vegetable chemical Oil, and gently warm this Mixture, the Oil by the Warmth mixes intimately with the Sulphur, lowers its Consistence, and makes it readily take fire by Flame. In these Operations, notwithstanding I always made use of the finest scented Oils of Orange Peel, Lemons, and such like, yet upon the least warming the Mixture, the rank Smell of Balsam (_i. e._ the ready Solution) of Sulphur was very obvious.

Read before the R. S.
_Oct. 24. 1745_.

_A Continuation of the Above._

Read, _Feb. 6. 1745_.

AS Water is a non-electric, and of Consequence a Conductor of Electricity, I had Reason to believe that Ice was endowed with the same Properties. Upon making the Experiment I found my Conjectures not without Foundation; for upon electrifying a Piece of Ice, wherever the Ice was touched by a non-electric, it flashed and snapped. A Piece of Ice also held in the Hand of an electrified Man, as in the beforementioned Processes, fired warm Spirit, chemical vegetable Oils, Camphor, and Gunpowder prepared as before. But here great Care must be taken, that by the Warmth of the Hand, or of the Air in the Room, the Ice does not melt; if so, every Drop of Water therefrom considerably diminishes the received Electricity. In Order to obviate this, I caused my Assistant, while he was electrifying, to be continually wiping the Ice dry upon a Napkin hung to the Buttons of his Coat, and this being electrified as well as the Ice, prevented any Loss of the Force of the Electricity. The Experiment will succeed likewise, if, instead of the Ice, you electrify the Spirit, _&c._ and bring the Ice not electrified near them. I must observe, that Ice is not so ready a Conductor of Electricity as Water; so that I very frequently have been disappointed in endeavouring with it to fire inflammable Substances, when it has been readily done by a Sword or the Finger of a Man.

In the first Paper[3] I had the Honour to lay before you upon this Subject, I took Notice of my having observed two different Appearances of the Fire from electrified Substances; _viz_. those large bright Flashes, which may be procured from any Part of electrified Bodies, by bringing a Non-Electric unexcited near them, and with which we have fired all the inflammable Substances mentioned in the Course of these Observations; and those, like the firing of wet Gunpowder, which are only perceptible at the Points or Edges of excited Non-electrics. These last also appear different in Colour and Form according to the Substances from which they proceed: For from polished Bodies, as the Point of a Sword, a Silver Probe, the Points of Scissors, and the Edges of the Steel-bar made Magnetical by the ingenious Dr. _Knight_, the electrical Fire appears like a Pencil of Rays, agreeing in Colour with the Fire from _Boyle_'s Phosphorus; but from unpolished Bodies, as the End of a Poker, a rusty Nail or such-like, the Rays are much more red. The Difference of Colour here, I am of Opinion, is owing rather to the different Reflection of the electrical Fire from the Surface of the Body from which it is emitted, than to any Difference in the Fire itself. These Pencils of Rays issue successively as long as the Bodies, from which they proceed, are exciting; but they are longer and more brilliant, if you bring any Non-Electric not excited near them, though it must not be close enough to make them snap. If you hold your Hand at about two or three Inches Distance from these Points, you not only feel successive Blasts of Wind from them, but hear also a crackling Noise. Where there are several Points, you observe at the same Time several Pencils of Rays.

* * * * *

IT appears from Experiments, that besides the several Properties, that Electricity is possess'd of peculiar to itself, it has some in common with Magnetism and Light.

PROPOSITION I.

IN common with Magnetism, Electricity counteracts, and in light Substances overcomes the Force of Gravity. Like that extraordinary Power likewise, it exerts its Force _in Vacuo_ as powerfully as in open Air, and this Force is extended to a considerable Distance through various Substances of different Textures and Densities.

COROLLARY.

GRAVITY is the general Endeavour and Tendency of Bodies towards the Center of the Earth; this is overcome by the Magnet with Regard to Iron, and by Electricity with Regard to light Substances both in its Attraction and Repulsion; but I have never been able to discern that vortical Motion, by which this Effect was said to be brought about by the late Dr. _Desaguliers_ and others, having no other Conception of its Manner of acting than as Rays from a Center, which indeed is confirmed by several Experiments. One of which, very easy to be tried, is, that if a single downy Seed of Cotton Grass is dropped from a Man's Hand, and in its Fall comes within the Attraction of the rubbed Tube; the Down of this Seed, which before seemed to stick together, separates, and forms Rays round the Center of the Seed: Or if you fasten many of these Seeds with Mucilage of Gum Arabic, round a Bit of Stick, the Down of them when electrified, which otherwise hangs from the Stick, is raised up, and forms a circular Appearance round the Stick. As these light Bodies are directed in their Motions, only by the Force impressed upon them, and as their Appearance is constantly _radiatim_, such Appearance by no Means squares with our Idea of a Vortex. Some have imagined a Polarity also, when they have observed one end of an excited Glass Tube repel light Substances, and the other attract them. But this Deception, arising from the whole Length of the Tube not being excited, but only such Part of it as has been rubbed; so that as much of the Tube as is held in the Hand, remains in an unexcited State, and permits light Substances to lie still thereon, though forcibly repell'd at the other End. This attractive Power of Electricity acts not only upon Non-electrics, as Leaf-Gold, Silver, Thread, and such like, but also upon originally Electrics, as Silk, dry Feathers, little Pieces of Glass and Resin; it attracts all Bodies, that are not of the same Standard of Electricity, (if I may be allowed the Expression) as the excited Body from which it proceeds. I have found no Body however dense, whose Pores are not pervious to Electricity by a proper Management, not even Gold itself.

PROPOSITION II.

IN common with Light, Electricity pervades Glass, but suffers no Refraction therefrom; I having from the most exact Observations found its Direction to be in right Lines, and that through Glasses of different Forms, included one within the other, and large Spaces left between each Glass.

COROLLARY.

THIS rectilineal Direction is observable only as far as the Electricity can penetrate through unexcited Originally-electrics, and those perfectly dry; nor is it at all material, whether these Substances are transparent, as Glass; semidiaphanous, as Porcelain or thin Cakes of white Wax; or quite opake, as thick woollen Cloth, as well as woven Silk of various Colours; it is only necessary that they be Originally-electrics. But the Case is widely different with Regard to Non-electrics; wherein the Direction, given to the Electricity by the excited originally-electric, is alter'd as soon as it touches the Surface of a Non-electric, and is propagated with a Degree of Swiftness scarcely to be measured in all possible Directions to impregnate the whole Non-electric Mass in Contact with it, or nearly so, however different in itself, and which must of Necessity be terminated by an originally Electric, before the Electricity exerts the least Attraction, and then this Power is observed first at that Part of the Non-electric the most remote from the originally-electric. Thus for Example, by an excited Tube held over it, Leaf Gold will be attracted through Glass, Cloth, _&c._ held horizontally in the Hand of a Man standing upon the Floor, and this Attraction is exerted to a considerable Distance. On the contrary, the rubbed Tube will not attract Leaf Gold or other light Bodies, however near, through Silver, Tin, the thinnest Board, Paper, or any other Non-electric, held in the Manner before-mentioned. But if you rub the Paper over with Wax melted, and by that Means introduce the originally-electric therein, you observe the Electricity acts in right Lines, and attracts powerfully. And here I must beg Leave to remind you, not only of the former Corollary, but of some of the former Experiments also; by which it appears, that although, to make a Non-electric exert any Power, we must excite the whole Mass thereof, yet we can excite what Part, and what only, of an originally-electric we please. Thus we observe, that Leaf-gold, and the Seed of Cotton-grass, (which grows upon Boggs and is a very proper Subject for these Inquiries) are attracted under a Glass Jar made warm[4], and turned Bottom upwards, upon which are placed Books and several other Non-electrics; and that the Motions of the light Bodies underneath correspond with the Motions of the Glass Tube held over them, the Electricity seeming instantaneously to pass through the Books and the Glass. But this does not happen, till the Electricity has fully impregnated the Non-electrics, which lie upon the Glass, which received Electricity is stopped by the Glass, and then these Non-electrics dart their Power directly through the upper Part of the Glass after the Manner of Originally-electrics. But if the thinnest Non-electric, even the finest Paper, as I before mentioned, is held in the Hand of a Man at the smallest Distance over the Leaf-Gold, and the Electricity is not stopped, not the least Power will be exerted, and the Gold will lie still. I must here remark likewise, that this Law of Electricity is so constant and regular, that I have not found one Deviation from it; so that even the Quicksilver, spread thin as it usually is at the Back of a Plate of a Looking-glass, will prevent the passing through of the electrical Attraction, unless stopped by an Originally-electric. This Penetration of the electrical Power through originally-electrics is much greater than has hitherto been imagined, and has caused the Want of Success to great Numbers of Experiments. I have been at no small Pains to determine, how far this Power can penetrate through a dry Originally-electric; and have found by repeated Trials, that either in a Cake of Wax alone, or of Wax and Resin mixed, when the Electricity is very powerful, it has passed, I say, in straight Lines through these Cakes of the Thickness of 2 Inches and 4/10; but I never could make it act through one of 2 Inches 8/10, for in this it was perfectly stopped. So that the Cakes commonly made use of to stop the Electricity, by being too thin, suffer a considerable Quantity of the electrical Power to pervade them, and be lost in the Floor. I make no Doubt, if the electrical Power could be more increased, it would penetrate much further through these Originally-electric Bodies.

PROPOSITION III.

ELECTRICITY, in common with Light likewise, when its Forces are collected and a proper Direction given thereto upon a proper Object, produces Fire and Flame.

COROLLARY.

THE Fire of Electricity (as I have before observed) is extremely delicate, and sets on Fire, as far as I have yet experienced, only inflammable Vapours. Nor is this Flame at all heightned by being superinduced upon an Iron Rod, red hot with coarser culinary Fire, as in a preceeding Experiment; nor diminished by being directed upon cold Water. However I was desirous of knowing, if this Flame would be effected by a still greater Degree of Cold; and in order to determine this, I made an artificial Cold; by which the Mercury, in a very nice Thermometer adjusted to _Fahrenheit_'s Scale, was depressed in about 4 Minutes from 15 Degrees above the freezing Point to 30 Degrees below it, that is, the Mercury fell 45 Degrees. From this cold Mixture, when electrified, the Flashes were as powerful and the Stroke as smart as from the red hot Iron. I could have made the Cold more intense, but the above was sufficient for my Purpose. This Experiment seems to indicate, that the Fire of Electricity is affected neither by the Presence or Absence of other Fire. For as red hot Iron, by Sir _Isaac Newton_'s Scale of Heat, is fixed at 192 Degrees, and as the Ratio between Sir _Isaac_'s Degrees and _Fahrenheit_'s is as 34 to 180, it necessarily follows, that the Difference of Heat between the hot Iron and the cold Mixture is 1040 Degrees; and nevertheless this vast Difference makes no Alteration in the Appearance of the electrical Flame. We find likewise, that as the Fire, arising from the Refraction of the Rays of Light by a _Lens_, and brought to a _Focus_, is observed first at some small Distance from their Surfaces, to set on Fire combustible Substances; the same Effect, as I have before observ'd, is produced in like Manner by electrical Flame.