If there are a number of generators of electricity in a circuit, whose electromotive forces in volts are E_1, E_2, etc., and if there are also opposing electro-motive forces. F_1, F_2, etc., volts, and if C is the current in webers, R the whole resistance of the current in ohms, P the total horse-power taken at the generators, Q the total horse-power converted into some other form of energy, and given out at the places where there are opposing electro-motive forces, H the total horse-power wasted in heat, because of resistance, then: (E_1+E_2+etc.)-(F_1+F_2+etc.) C = ----------------------------- R [TEX: C = \frac{(E_1+E_2+\text{etc.})-(F_1+F_2+\text{etc.})}{R}] C C P = ---((E_1+E_2+etc.); Q = ---(F_1+F_2+etc.) 746 746 [TEX: \frac{C}{746}(E_1+E_2+\text{etc.});\ Q = \frac{C}{746}(F_1+F_2+\text{etc.})] C² R H = ----- . 746 [TEX: H = \frac{C^2 R}{746}.] The lifting power of an electro-magnet of given volume is proportional to the heat generated against resistance in the wire of the magnet. The future of many electrical appliances depends on how general is the public comprehension of the lessons taught by these wall sheets. If a few capitalists in London would only spend a few days in learning thoroughly what these mean, electrical appliances of a very distant future would date from a few months hence. A number of experiments were shown, in some of which electrical energy was converted into heat, in others into sound, in others into work. At this part of the lecture reference was made to the work of Prof. Ayrton and his pupils at Cowper street (City and Guilds of London Institute Classes). They measure (1) the gas consumed by the engine, (2) the horse-power given to the dynamo machine, (3) the current in the circuit in webers, and (4) the resistance of the circuit. Thus exact calculations can now be made as to the horse power expended in any part of the circuit, and the light given out in any given period by an electric lamp. The dynamometers used in these measurements were described, but at present, in some cases, the description given is for various reasons incomplete, so that we shall take a future opportunity of writing of these instruments. To measure the light a photometer, constructed by Profs. Ayrton and Perry, is used, which obviates the necessity of large rooms, and enables the operator to give the intensity in a very short period of time. A number of measurements of the illuminating power of an electric lamp were rapidly made during the lecture with this photometer. By means of a small dynamo machine, driven by an electric current generated in the Adelphi arches, a ventilator, a sewing machine, a lathe, etc., were driven; in the latter a piece of wood was turned. "What," said the lecturer, "do these examples show you?" "They show that if I have a steam-engine in my back yard I can