tricity always efcapes from that part of the furface, where the powers are moft feparated. The fpark is of a different colour according to the density; when it is rare, it appears of a bluish colour; when more denfe, it is purple; when highly condenfed, it is clear and white like the light of the fun. The middle part of an electric fpark, when the two powers meet, often appears diluted, and of a red or violet colour, the ends are more vivid and white; when very strong, it will branch out and divide into many parts.

OF MOTIONS PRODUCED BY THE ELECTRIC

STREAM.

Whenever there is an efflux of one power of electricity, there is alfo an afflux of the other power, if any conducting fubftance is placed fo near and in fuch circumftances, as that it can be drawn therefrom.

Here is a brafs crofs, fig. 5, pl. 2, fupported on a point like a compafs needle, with each of it's points bent the fame way; place this upon the conductor, and as foon as I turn the machine, it turns with great rapidity, but always from the points, because the electric fire flying off from the points, acts forcibly on the air, and is confequently re-acted upon, which occafions the motion. Take the fly and it's point, and hold it in your hand under the conductor, and it will turn in the fame manner, by a stream of electricity of a contrary power to that thrown off from the conductor, which is drawn in from you and delivered from the points of the fly to the conductor. Now infulate the fly, and place it at the fame diftance from the conductor, and it will not move, becaufe no electricity can be drawn through it; but hold a pin near it, and the fly will immediately begin to turn, as it

draws

wards this drop, long zig-zag Sparks are obtained from the drop of water; the drop takes a conical figure; my knuckle is wetted. The spark was confiderably longer than could be obtained from the conductor without the water.

Faften a piece of good fealing-wax to the ball on the end of the conductor, but place it in fuch a manner that it may be eafily fet on fire by a taper; fet it on fire while I turn the machine; the wax becomes pointed, and fhoots out an almost invifible thread to a confiderable diftance. If you receive the filaments on a fheet of paper, the paper will be covered in a very curious manner by the electrified wax threads; the wax flying to thofe places where it can unite with the contrary power.

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LECTURE

OF THE DIFFUSION AND SUBDIVISION OF FLUIDS BY ELECTRICITY.

From experiments made by Abbé Nollet, it appears, that electricity augments the natural evaporation of moft fluids, particularly of those which have the greatest tendency to evaporate; that it, in this refpect, acts moft powerfully upon the fluids when they are contained in metal veffels; but it never makes any fluids evaporate through the pores either of metal or glafs. When fluids, that are paffing through capillary tubes, are electrified, the ftream is fubdivided; and if the tube be less than of an inch in diameter, their motion is generally accelerated.

I fufpend this metal phial (to the bottom of which a capillary tube is adapted) to the conductor; before I turn the cylinder, the tube carries off the water only by interrupted drops; but on turning the cylinder, and electrifying the water, the dropping from the tube is changed into a continued ftream. On applying my finger to the conductor, the electricity is interrupted, and the water again only defcends in drops: my finger taken away, the water runs in a diverging ftream: darken the room, and you perceive a fiery stream defcend from the tube. This experiment has been termed the electrical jet de feu.

Infulate two pails with capillary tubes; connect one with the cushion, the other with the conductor; turn the machine, and the water, which is difperfed into very minute particles, when they are near enough, is brought together by the effort of the two powers to join each other; the drops coalefce and come down like a heavy fhower of rain.

I place a drop of water on the conductor, and turn the machine. On prefenting my knuckle toVOL. IV.

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wards

wards this drop, long zig-zag Sparks are obtained from the drop of water; the drop takes a conical figure; my knuckle is wetted. The spark was confiderably longer than could be obtained from the conductor without the water.

Faften a piece of good fealing-wax to the ball on the end of the conductor, but place it in fuch a manner that it may be easily fet on fire by a taper; fet it on fire while I turn the machine; the wax becomes pointed, and fhoots out an almost invisible thread to a confiderable diftance. If you receive the filaments on a sheet of paper, the paper will be covered in a very curious manner by the electrified wax threads; the wax flying to thofe places where it can unite with the contrary power.

LECTURE

LECTURE XLVII.

OF THE LEYDEN PHIAL,

DR. PRIESTLEY has well obferved, that electricity has one advantage over most other branches of natural philofophy: it furnishes matter of entertainment for all perfons promifcuously, while it is also a fubject of important fpeculation for the most philofophic minds. Neither the airpump, nor the orrery, nor any experiments in hydroftatics, optics, or magnetifm, &c. ever brought together fo many, or fuch great concourfes of people, as thofe of electricity have fingly done.

If you only confider what it is in objects that makes them capable of exciting that pleafing afonifhment which has fuch charms for all mankind, you will not wonder at the eagerness with which perfons of both fexes, and of every age and condition, run to fee electrical experiments. For here you fee the courfe of nature overturned to all appearance, and by caufes feemingly inconfiderable.

For it exhibits to you bodies rifing and falling, moving this way and that, and fufpended by others contrary to the principles of gravitation, and this by powers which have been put in action only by a very flight friction. Here you may fee a piece of cold metal, or even water or ice, emitting frong fpara of fre, fo as to be able to kindle many infammable fibffantes. Nor will you find any thing more affontihing then wait I am going You will End a common gas jar, after a little preparation, capable of going a peilio look a violent fenation, is nothing elfe in me, and that the diharge of the bot

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