A stick of sealing-wax or a bit of glass tube, perfectly dry, rubbed against a warm piece of flannel, has elicited upon its surface a new power, which will attract bits of paper, straw, or other light materials; and after these substances are endowed with the same force, a repellent action takes place, and they fly off. One of the most convenient arrangements for making experiments with the attractive and repellent powers of electricity is to fix with shell-lac varnish round discs of gilt paper, of the size of a half-crown, at each end of a long straw that is supported about the centre with a silk thread, which may hang from the ceiling or any other convenient support. (Fig. 160.) [Illustration: Fig. 160. A. The glass pillar support. B. Straw with discs, hanging by a silk thread.] The varnish is easily prepared by placing four or eight ounces of shell-lac in a bottle, and pouring enough pyroxylic spirit (commonly termed wood naphtha) upon the lac to cover it. After a short time, and by agitation, solution takes place. In a variety of ways friction is proved to be a source of electricity, and forms a distinct branch of the science, under the name of _frictional_ electricity. _Second Experiment._ The nature of chemical action has been already explained, and is alluded to here as a source of electricity of which the proof is very simple. A piece of copper and a similar-sized plate of zinc have attached to them copper wires; these plates are placed opposite to, but do not touch each other, in a vessel containing water acidulated with a small quantity of sulphuric acid. When the wires are brought in contact, a current of electricity circulates through the arrangement, but has no power to attract bits of paper, straw, &c. In order to ascertain whether the current of electricity passes or not, a piece of covered copper wire is bent several times round a magnetic needle, so that it has freedom of motion inside the core or hollow formed by twisting the copper wire. This arrangement, properly constructed, is called the galvanometer [Page 176] needle, and is invaluable as a means of ascertaining the passage of electricity derived from chemical action. (Fig. 161.) [Illustration: Fig. 161. A. The galvanometer needle. B. Vessel containing weak acid and the zinc and copper plates. The arrows show the path of the electric current.] When the wires leading from the metal plates are connected with the extremities of the coil in the galvanometer, the needle is deflected or pushed aside to the right hand or to the left, according to the direction of the current. _Third Experiment._