Part 3
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.
I MAY perhaps be thought too minute in some of the before-mentioned Particulars; but in Inquiries abstruse as these are, where we have so little _a priori_ to direct us, the greatest Attention must be had to every Circumstance, if we are truly desirous of investigating the Laws of this surprizing Power. For, as has been said upon another Occasion by my ever honoured Friend MARTIN FOLKES, Esq; our most worthy President, "that Electricity seems to furnish an inexhaustible Fund for Inquiry; and sure Phænomena so various and so wonderful can arise only from Causes very general and extensive, and such as must have been designed by the Almighty Author of Nature for the Production of very great Effects, and such as are of great Moment to the System of the Universe."
IF these Observations receive the Countenance of this learned Society, I shall think myself sufficiently recompensed, and am,
_Gentlemen, with the highest Esteem,_ _your most Obedient_ _humble Servant_, W. WATSON.
_FINIS._
Footnote 1:
Dr. _Gowin Knight_, F. R. S.
Footnote 2:
I call _Electrics per se_ or originally-_electrics_, those Bodies, in which an attractive Power towards light Substances is easily excited by Friction; such as Glass, Amber, Sulphur, Sealing-wax, and most dry Parts of Animals, as Silk, Hair, and such like. I call _Non-electrics_ or Conductors of Electricity, those Bodies, in which the above Property is not at all or very slightly perceptible; such as Wood, Animals living or dead, Metals and vegetable Substances. See _Gray_, _Du Fay_, _Desaguliers_, _Wheler_, in the Philosophical Transactions.
Footnote 3:
Page 6.
Footnote 4:
I have constantly observed, that the electrical Attraction through Glass is much more powerful, when the Glass is made warm, than when cold. This Effect may proceed from a two-fold Cause: First, warm Glass does not condense the Water from the Air, which makes the Glass, as has been before[5] demonstrated, a Conductor of Electricity: secondly; As heat enlarges the Dimensions of all known Bodies, and consequently causes their constituent Parts to recede from each other, the electrical Effluvia, passing in straight Lines, find probably a more ready Passage through their Pores.
Footnote 5:
Page 13.
Transcriber's note:
All footnotes moved to the end of the text.
Page 5, 'Contract' changed to 'Contact,' "the Contact of Non-electrics..."
Page 6, 'Power' changed to 'Poker,' "I suspended a Poker in silk Lines;"
Page 7, second 'it' struck, "if it does..."
Page 9, 'o'Clock' rejoined.
Page 9, period added to 'E. N. E.'
Page 22, 'erectified' changed to 'electrified,' "and a Person not electrified..."
Page 49, 'it' changed to 'itself,' "not even Gold itself."