Notice sur des Expériences exécutées avec la Machine Dynamo-électrique
et avec la Lampe á arc Voltaïque de M. Jürgensen

17 Report on the Jürgensen dynamo machine and lamp. 68, Sloane Street, S. W. September 4th, 1882. We have made a large number of experiments with this machine at different speeds, and sending currents through various resistances. In each case there were measured: 1. The horse-power actually given to the dynamo. 2. The speed of rotations of the dynamo. 3. The current in amperes generated. 4. The electromotive force in volts set up between the terminals of the machine. We find that for currents of over 15 amperes at the lower speeds of 500 to 600 revolutions per minute, and for currents of over 12 amperes at the higher speeds of 750 to 950 revolutions, the efficiency of the machine was half, or more; that is to say, for every horse-power given by the engine to the dynamo at least one-half a horse-power was electrically given out by it, part of this being given out in the external circuit, and part appearing as heat in the armature and field magnets of the machine itself. At a speed of 790 revolutions per minute, when the external resistance was equel to 3,9 ohms, the effi- ciency of the machine reached 0,93 and the useful effi- ciency to 0,54, that is to say, of the horse-power given by the engine to the dynamo 93 per cent, was given out electrically by the dynamo, 54 per cent, appearing in the external circuit. In this case the actual horse-power given to the dynamo was 4,9, of which 4,6 was reproduced electri- cally by the machine, 2,6 of this appearing in the exter- nal circuit. 2