That the difficulty in the use of an intermittent current may be more clearly understood, I shall ask you to accompany me in my explanation of the effect produced when two musical signals of different pitch are simultaneously directed along the same circuit. Fig. 11 shows an arrangement whereby the reeds _a a´_ of two transmitting instruments are caused to interrupt the current from the same battery, B. We shall suppose the musical interval between the two reeds to be a major third, in which case their vibrations are in the ratio of 4 to 5, _i.e._, 4 vibrations of _a_ are made in the same time as 5 vibrations of _a^1_. A^2 and B^2 represent the intermittent currents produced, 4 impulses of B^2 being made in the same time as 5 impulses of A^2. The line A^2 + B^2 represents the resultant effect upon the main line when the reeds _a_ and _a^1_ are simultaneously caused to make and break the same circuit, and from the illustration you will perceive that the resultant current, whilst retaining a uniform intensity, is less interrupted when both reeds are in operation than when one alone is employed. By carrying your thoughts still further you will understand that when a large number of reeds of different pitch or of different rates of vibration are simultaneously making and breaking the same circuit the resultant effect upon the main line is practically equivalent to one continuous current. [Illustration: Fig. 11.] It will also be understood that the maximum number of musical signals that can be simultaneously directed along a single wire without conflict depends very much upon the ratio which the “make” bears to the “break;” the shorter the contact made, and the longer the break, the greater the number of signals that can be transmitted without confusion, and _vice versâ_. The apparatus by means of which this theoretical conclusion has been verified is here to-night, and consists of an ordinary parlour harmonium, the reeds of which are operated by wind in the usual manner. In front of each reed is arranged a metal screw, against which the reed strikes in the course of its vibration. By adjusting the screw the duration of the contact can be made long or short. The reeds are connected with one pole of a battery, and the screws against which they strike communicate with the line-wire, so that intermittent impulses from the battery are transmitted along the line-wire during the vibration of the reeds. [Illustration: Fig. 12.] [Illustration: Fig. 13.] [Illustration: Fig. 14.]