Lectures on electricity / by James Ferguson, F.R.S.

  • James Ferguson
Date:
1825
Catalogue details

Licence: Public Domain Mark

Credit: Lectures on electricity / by James Ferguson, F.R.S. Source: Wellcome Collection.

    19/112 (page 15)
    lining which covers the inside of the bottom of the jar ; and a smooth ball a is fixed on the top of the wire, which must be of such a height as to touch the ball of the prime conductor when the jar is set near enough to it on the table.—B is the discharger, which is made of strong brass wire, bent into the form of part of a circle ; and has two balls c and d fixed on its ends. N. B. The brass ball on the tops of all the wires belonging to the several jars ought to be of equal height when they are set upon a table. The thinner these jars are, they are so much the better for electrical experiments. The coating and lining are generally fixed to them with thick starch, or bookbinder’s paste ; but I find that thick varnish, such as is used by coachmakers, does better for that purpose, and dries immediately, which the other does not. 24. In Fig. 3, A is just such a jar as the one above described; only it has an additional wire B, bent into the form of a ring, so as to fit the outside, and remain on any part of the coating over which it is placed; with a brass ball D on its top, of equal height with the ball C from the table. E is a bit of cork, cut in to the form of a spider, with legs of linen thread, fixed into it by draw- ing them through with a small needle, and then cut with scissars to a proper length. It is hung by a silk thread to the ceiling of the room, and at such a height above the table that its legs may touch the balls C and D, if it be made to swing between them. Before the legs are put to it, it must be put upon the point of a wire, and turned round and round in the flame of a candle, to burn off the roughness and sharp edges which the knife had left on its surface ; and then the burnt parts must be rubbed off between a wet finger and thumb, to smooth.it. 25. In Fig. 4, A a is a thin glass, blown into the shape of a Florence flask, left open at the small end a. A cork, through which a small hole has been made by