622 SCIENTIFIC EECORD FOR 1883. 



act optically, the shadow being sharply defined. By rotating a per- 

 forated iron disk between a magnet and a coil with an iron core, a sound 

 was heard in a telephone in circuit corresponding in pitch to the num- 

 ber of perforations which passed per second. When the disk had two 

 rows of holes, one of thirty-two, the other of sixty-four, the interval, 

 heard was the octave. He calls the instrument the magnetophone. 

 (Nature, October, xxviii, G26.) 



Bosanquet has given a valuable discussion of the theory of the com- 

 pound dynamo-machine, i. e., one that has its field wound with two coils, 

 one in the main and the other in the shunt circuit. His Gramme 

 dynamo, with field coils in main circuit, failed whenever more than ten 

 ohms was put in the external circuit. Consequently, he wound 2,000 

 turns of a small wire on pasteboard cylinders, fitting over the main coils, 

 the resistance of these auxiliary coils being about 27 ohms. The ends 

 of this coil are attached to the armature brushes, and even when the 

 main circuit is open an electromotive force of 70 to 80 volts is produced 

 by the machine. The advantages of this alteration are obvious. (Phil. 

 Mag., April, 1883, V, xv, 275.) 



The question of the transmission of power electrically has absorbed 

 a large share of attention. On March 15, Siemens gave a lecture on 

 this subject at the Institution of Civil Engineers, giving an interesting 

 resume" of the progress of scientific thought on the subject and a his- 

 torical sketch of the development of electric railways. (Nature, March, 

 1883, xxvn, 518.) Tresca has made a report to the French Academy 

 upon the transmission of power from Paris to Bourget by the system 

 of Deprez. The distance from one station tQ the other and back was 

 17 kilometers. The electric energy was transmitted over an ordinary 

 telegraph wire 4 mm . in diameter, having a resistance of 1G0 ohms. 

 The motive power absorbed by the generator was G.21 horsepower; 

 that yielded to the brake by the motor was 2.03 horse-power, or 32.7 

 per cent. The generator made 588 revolutions a minute, and gave an 

 electromotive force of 1,290.5 volts. (C. B.. February, 1883, xevi, 457.) 

 In a second set of experiments the generator made 814 revolutions ; the 

 electromotive force developed was about 2,000 volts, the power con- 

 sumed 10.395 horse-power, and recovered 3.304 ; giving an efficiency for 

 the system of 31.7 per cent. (C. P., xevi, 530.) The Academy then ap- 

 pointed a commission, with Cornu as secretary, to repeat the experi- 

 ments. With a speed of 850 turns, 9.514 horse-power was absorbed 

 by the generator, and 3.582 returned by the motor ; a yield of 37.5 per 

 cent. The electromotive force was 1,937 volts. (Ann. Ghim. Phys., Oc- 

 tober, 1883, V, xxx, 214.) 



The production of power from accumulators has also made some prog- 

 ress. An electrical tram-car was tried at Kew in March. The battery 

 is placed under the seats, and consists of fifty Faure-Sellon- Volckmar 

 cells, each 13 by 11 by 7 inches, and weighing 80 pounds. It is capable of 

 driving the full car for seven hours. (Nature, March, 1883, xxvn, 470.) 



