To produce all the requisite signals with a single pith-ball electrometer, it was necessary to vary the durations of each divergence, and to combine several to form a single symbol. Thus, suppose that a single divergence of the pith-balls for a second was understood to signify the letter _A_; one divergence, followed by an immediate collapse, by discharging the electricity, might signify _B_; two prolonged divergences might signify _C_, and two short ones _D_; and by thus increasing the number and varying the divergences of the two pith-balls, all the letters of the alphabet might be indicated. A still more direct method of representing the letters of the alphabet was proposed by M. Reizen in 1794, by the application of the means frequently adopted for exhibiting the light of the electric spark. The charge of a Leyden jar was sent through strips of tin foil, pasted on to a flat piece of glass, so as to form several lines, joined at the ends alternately into a continuous circuit. Interruptions were made in the foil by cutting small portions away, at which points brilliant sparks appeared when the jar was discharged. As the interruptions were so contrived as to form letters, and the strips of tin foil were all arranged separately on a long pane of glass, any letter required could be distinctly made visible by discharging the jar through that particular circuit. To produce all the letters of the alphabet in this manner, a separate circuit was required for each. Another plan, far less feasible, and scarcely deserving of notice, excepting for its peculiarity, was proposed in the following year by M. Cavallo, who suggested the setting fire to combustibles, or the explosion of detonating substances, as the means of signalling intelligence. About the same time several attempts were made by electricians in Spain to transmit signals by electricity, but their plans were not more practicable than those already mentioned, and depended for their effects on the discharge of Leyden jars. The discovery of voltaic electricity at the beginning of the present century was an important step in the progress of the Electric Telegraph, though several years elapsed before the applicability of the discovery for that purpose became known; and it was not fully appreciated till within the last twenty years.