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

23 periment the dynamo was not heated, the temperature was found not to exceed 30° C, a temperature so low, that it can be in no way of damage to any part of the machine. During the electrical Exhibition held in Paris in 1881, the different dynamos and arc lamps were sub- jected to numerous tests by a special commission: Messrs. Allard, Joubert, Le Blanc, Potier and Tresca; in novem- ber 1882 the results obtained were made known to the „académie des sciences“ in a report, the most complete regarding this sort of experiments. The measurements, though taken with great care, are not quite inseparable from local influences; by seve- ral tests it was necessary to introduce resistances in the circuit, to weaken the intensity of the current, the room not being large enough to permit measurements of the light, produced by the original current, to be taken by means of a photometer, without weakening the intensity of the current. The commission therefore points out, that among the results, published in the report, special weight is to be ascribed to the numbers representing the total efficiency of the different dynamos, these results being independent of the local influences. Of the many dynamos subjected to these tests the Jürgensen dynamo-machine in this respect takes a pre- dominant place, 97 per Gent, of the horse-power, given by the engine to the dynamo, being given out electri- cally by the dynamo; the Bürgin and the Weston dynamo were found to give 95 per Cent., a dynamo of Siemens 94 p. C., one of Gramme 92 p. C., of Maxim 91 p. C. and one of Brush 85 p. C. A useful efficiency as great, as that given by the Jürgensen dynamo-electric machine, lias not even approxi-