27 The Couronne de fig 269 lasses is one of the sim- plest kinds of compound battery; and was invented by Volta.

It consists of any number of glass cups A, B, and D, fig 269, con- taining dilute acid, in which are immersed zinc and copper plates con- nected together.

Wires P and N, attached to the terminal plates, are very often called the poles [10] of a battery.

28 Volta s pile, or column, fig 270, is formed with discs of zinc, copper, and cloth, wetted with dilute acid, and built up in the same order.

They are retained in their places by glass rods.