First, rub the thick packing paper over a hot fire or a stove, and the friction must be continued for some time, until the paper has become thoroughly dry, and as hot as possible without charring. When this has been accomplished, place it quickly upon a wooden table, and rub it rapidly and energetically with a clothes’ brush, dry and hard as can be obtained. Place the paper upon the tray; touch the tray with the knuckle, and draw away the paper by the handles fixed to it (_see_ fig. 201); a spark will result. Then if the paper be replaced upon the tray, and the hand again presented, the same result will follow. This experiment may be repeated five or six times, at least, with success. We have in this tea-tray and its paper covering a real electric machine. How can we manage to provide a Leyden jar to contain our electricity? Nothing is more easy. Let us take a tumbler and partly fill it with shot; insert into the glass a tea-spoon, and if all the articles are quite dry we shall possess a Leyden jar. To charge the jar we have thus provided we must work the Electrophorus we have already described. While one person lifts off the paper as directed, another must hold the glass filled with shot close to the edge of the tray, and touch the corner with the tea-spoon; the spark will then enter the “jar” or tumbler. We can thus charge the jar as we please, and by presenting the finger as in the illustration (fig. 202), we shall obtain a discharge from it. [Illustration: Fig. 202.—A Leyden jar.] Mr. Louis Figuier, in his “_Merveilles de la Science_,” relates that Wollaston, meeting one of his friends one evening in the streets of London, drew from his pocket a copper thimble, and proceeded to turn it into a microscopic pile.[13] In order to do this he removed the bottom of the thimble, flattened it with a stone, so as to bring the two internal surfaces about on a line with each other, then placed between the copper surfaces a small strip of zinc, which was not in contact with the copper, owing to the interposition of a little sealing-wax. He then placed it in a glass cup, previously filled with the contents of a small phial of water, acidulated with sulphuric acid. He next wound round the strip of zinc and its copper covering a piece of platinum wire, the wire becoming red through the electricity developed in the pile. The dimensions of this platinum wire were extremely small; it was only 30/1000 of an inch in diameter, and 1/30 of an inch in length. By reason of its small dimensions it could not only be reddened, but fused by the little battery. Thus Wollaston’s friend, who was a witness of the experiment, was able to light a tinder at the red wire. In this little battery of Wollaston’s the copper enveloped the strip of zinc in every part; that is to say, the negative element was on a higher surface than the positive metal. [Illustration: Fig. 203.-A simple compass.]