A Pith ball suspended from the centre rod of a charged Leyden jar provides us with an interesting and very delicate method of demonstrating the ionised atmosphere surrounding flames and incandescent bodies. In an ionised atmosphere of sufficient intensity the ball, provided that the suspending fibre is of high insulating quality, rapidly loses its charge and falls back toward the centre rod of the jar, from which it receives a fresh charge and is violently repelled, only to repeat the performance; thus an oscillation is set up the rapidity of which is governed chiefly by the length of the suspending fibre.