295] This part consists chiefly of experiments made to determine the charges of plates of glass and other electric substances coated in the manner of Leyden vials. The method I used in doing this was nearly of the same nature as that by which I determined the charges of the other sort of bodies in the preceding part, but the apparatus was more compact and portable and is represented in Fig. 20, where Hh is a horizontal board lying on the ground, Ll and Ll are two upright pillars supporting the two horizontal bars Nn and Pp, both at the same height above the ground, and parallel to each other.

To these two bars are fastened four upright sticks of glass covered with sealing wax; they are represented in the figure and shaded black, but are not distinguished by letters to avoid confusion. To these sticks of glass are fastened four horizontal pieces of wire Aa, Bb, Dd, and Ee, and to Bb is fastened another wire mM supported at the further end by a stick of waxed glass.

Rr is a wooden bar reaching from the wire Ee to the pillar Ll, and along the upper edge of this bar runs a wire, one end of which is wound round the wire Ee and the other reaches to the ground and serves to make a communication between Ee and the ground.