Much instructive amusement is afforded by testing the gold leaves when separated from each other during either of the former experiments, [Page 182] with an excited piece of sealing-wax. If the electricity produced is negative, they repel each other further when the excited wax is approached; if positive, they fall when the excited wax is brought near them. _Eighteenth Experiment._ When fresh, dry, ground coffee is received on to the disc of the electroscope, as it falls from the mill, powerful electrical excitation is displayed, and this is sometimes so apparent, that the particles cling around the lower part of the mill or to the sides of the cup or basin held to catch it. _Nineteenth Experiment._ After playing a tune on a violin, hold the bow (well rosined) to the electroscope, when the usual divergence of the leaves will be apparent. _Twentieth Experiment._ Cut some chips from a piece of wood with a knife attached to a glass handle, and as they fall on to the electroscope the leaves are repelled. _Twenty-first Experiment._ Warm a piece of bombazine by the fire and then draw out some of the threads (which are of two kinds--viz., silk and wool), and place them on the electroscope, when divergence of the leaves immediately takes place. _Twenty-second Experiment._ Put upon the same leg a worsted stocking and over that a silk one, if the latter is now quickly rubbed all over with a dry hand and near the fire, and then suddenly slipped off, the sides repel each other, and the silk stocking retains very much the same shape as if the leg still remained in it, and of course collapses as the electricity passes away. _Twenty-third Experiment._ Electrical machines consist only in the better arrangement of larger pieces of glass and a more convenient mechanical contrivance for rubbing them, and are of two kinds--viz., the cylinder and plate machines; it is usual to give directions for the manufacture of an electrical machine from a common bottle, and doubtless such rude instruments have been made, but as Messrs. Elliott Brothers, of 30, Strand, now supply excellent small machines at a very low cost, it is hardly worth while to incur even a small expense for an instrument that must at the best be a very imperfect one and frequently out of order. (Fig. 166.) [Page 183] [Illustration: Fig. 166. A cylinder electrical machine.] [Illustration: Fig. 167. The ordinary plate electrical machine.]