melted by the electric lightning, and driven into the very substance of the glafs.

A pane of glafs, coated on each fide, the coating being every where about two inches from the edge, with a picture pafted on the upper fide, and put into a frame, is called the magic picture; one line of tinfoil that goes from the coating of the under fide, is made to communicate with the bottom of the frame; the back edge of the bottom rail and the frame is covered with tinfoil. Set the face of the picture against the ball of the conductor, and turn the machine. Then take it away, and holding it in an horizontal pofition by the top of the frame, lay a fmall piece of money upon the head. You may then defire any perfon to take hold of the lower rail of the frame with one hand, and to take off the piece of money with the other; in attempting to do this, he will fail of his defign, for the moment he touches the money he will receive a strong fhock. You must continue to hold the frame all the while, and will have nothing to fear, becaufe none of the electric virtue, with which the picture is charged, can come to you, as you are not in the circuit.

This bottlcalled is the Spotted bottle, because it is only coated with fmall pieces of tinfoil, placed at a little diftance from each other; charge this bottle in the ufual manner, and you will fee ftrong sparks of electricity fly from one fpot of tinfoil to the other, making the paffage of the fluid on the outfide very vifibic. Difcharge this bottle, by bringing a pointed wire gradually near the knob, and the uncoated part of the glafs between the fpots will be pleafingly illuminated, and the noife will refemble that of fmall fired crackers. If the jar is difcharged fuddenly, the outfide furface appears illuminated. To produce thefe appearances, the glafs must be very dry.

Hold a phial in the hand which has no coat

ing on the outfide, and prefent it's knob towards an electrified conductor; the fire, while it is charging, will pass from the outfide to the hand, in a pleafing manner; on the difcharge, beautiful ramifications will be feen upon the uncoated part of the jar.

By fetting fire to fome tow in a tin house, you have a reprefentation of that awful appearance, a boufe in flames. To make this experiment fucceed, take a piece of soft tow, dry it well, and then rub, or fill it pretty well with rofin, and place it between the balls in the infide of the houfe; the balls fhould not be far afunder, nor the charge too high, connect the hook at the bottom of the house, with the bottom of the jar; let the top of the jar be connected with the conductor, and when it is charged, put one ball of the jointed discharger on the conductor, and bring the other down upon the ball above the houfe; the explosion will fet the tow on fire, whose flames will pass through the windows, and make the house appear like one on fire.

You may pleasingly illuftrate the nature of the Leyden phial, by fufpending two fets of bells therefrom; one fet connected with the infide, the other with the outfide, fee fig. 16, pl. 1. Hook up the chain from the bells communicating with the infide, that they may have no connection with the table; charge the bottle in the ufual manner; during the charge, the fet fufpended from the outfide will continue to ring. After the bottle is charged, unhook the wire of the bells fufpended from the infide. Touch now the wire A, and the bells will ceafe ringing, but the other fet will begin to act; take the finger from A, and apply it to B, and the bells at B will be quiet, while thofe at A will be fet in motion, and fo on alternately, till the bottle is difcharged.

EXPERIMENTS WITH THE ELECTRICAL BATTERY.

The moft formidable part of the electrical apparatus is the electrical battery, that is, a number of jars connected together in a box; the bottom of the box is covered with tin-foil; from these a hook projects on the outfide of the box, by which any fubftance may be connected with the outfide of the jars; their infides are all connected by wires.

With a battery you may perform a great number of very furprifing and interefting experiments; and though, if very large, it be a formidable appendage to an electrical machine, and ought always to be used with caution, yet it cannot be faid, that the apparatus of an electrician is complete without it; it's effects in rending various bodies, in firing gunpowder, in melting wires, and in imitating all the effects of lightning, never fail to be viewed with astonishment.

There is fome caution neceffary, in the use and management of a battery, and you fhould be careful never to make part of the circuit, and to prevent those that are feeing the experiments touching the battery, or approaching too near to any part of the apparatus; the quadrant electrometer fhould be always ufed with it; it is best to place it upon the ball, which unites the internal wires, but it fhould always be elevated two or three feet above the ball. A battery cannot be charged fo high in proportion, as a fingle jar; the quadrant electrometer, therefore, never rifes fo high as 90 degrees, feldom higher than to 60 or 70 degrees, more or lefs, in proportion to the fize of the battery, and the force of the machine. I must observe to you here, that if one jar in your battery be broke,

you

you must remove the broken jar, before the rest can be charged.

Mr. Atwood made, with his battery, a very curious experiment on the perforation of paper by the electric fluid, combined with thofe that I fhall afterwards relate to you, you will find it prove, with great clearness, the existence and action of the two electric powers.

He fufpended a quire of paper by a line, in the manner of a pendulum, from a convenient altitude, fo that it's plane might be vertical. The largest charge from a battery was paffed through it, while quiefcent in an horizontal direction perpendicular to the plane, the rods of communication not touching the paper; the phenomena were, first, the aperture mentioned in the leaves, being protruded both ways from the middle:* fecond, not the fmalleft motion was communicated to the paper from the force of the difcharge.

A quire of the thickeft and strongest paper was made ufe of for this experiment, the height from which it was fufpended fixteen feet. It is an extraordinary appearance on the hypothefis of a fingle electric fluid, that a force fufficient to penetrate a folid fubftance of great tenacity and cohefive force, fhould not communicate the smallest motion to the paper, when a breath of air would caufe fome fenfible vibration in it. But the other phenomenon, i.e. the oppofite direction in which the leaves are protruded, tends very much to ftrengthen the opinion of two oppofite currents; indeed when the two facts are taken together, it is fcarcely poffible to reconcile the hypothefis of a single power

with matter of fact.

Mr.

*The bur of the paper pointed one way on one fide, and the oppofite way on the other fide, as if the hole had been made in the quire, by drawing two threads through it, in a contrary direction.

Mr. Symmer placed in the middle of a paper book, of the thickness of a quire, a flip of tin-foil; in another of the fame thickness he put two flips of tin-foil, including the two middle leaves between them; upon paffing the electric stroke through them, he found the following effects. In the first, the leaves on the fide of the foil were pierced, while the foil itself remained unpierced; but at the fame time he could perceive, that an impref fion had been made on each of it's furfaces, at a fmall diftance from each other; fuch impreffions were still more visible on the paper, and might be traced as pointing different ways. In the fecond, all the leaves of the book were pierced, excepting the two holes that were between the flips of foil, and in these two, instead of holes, the two impreffions in contrary directions were vifible.

When a quire of paper, without any thing between the leaves, is pierced by the electrical ftroke, the two powers keep in the fame track, and make but one hole in their paffage through the paper; not but that the power from above, or that from below, fometimes darts into the paper at two or more different points, making fo many holes; but thefe generally unite before they go through the paper. They feem to pafs each other about the middle of the quire, for there the edges are moft visibly bent different ways; whereas, on the leaves near the outfide, the holes very often carry more the appearance of a power iffuing out, than of one darting into the paper.

When any thin metallic fubftance, fuch as gilt leaf, or tin-foil, is put between the leaves of the quire, and the whole is ftruck; the counteracting powers diviate from the direct track, and make their way in different lines to the metallic body, and strike it in two different points diftant from one another, about