170 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



ler, of Calcutta, was introduced, on the 28tli of January, 1875, 

 on one of the main lines from Calcutta to Bombay, 1600 

 miles ; since which time, and in the worst season the south- 

 west monsoon the method has worked with Qrreat resfulari- 

 ty and speed. In a few days another main line from Bom- 

 bay to Madras will be worked ; and it is probable that before 

 the lapse of the current year (1875) the whole of the main 

 traffic in India, from Calcutta to liangoon included, will be 

 carried on by this system. The method is also practicable 

 on cables, as shown by the experiments with the cable from 

 Bombay to Aden, 1800 miles long. It has been mathematic- 

 ally demonstrated and confirmed by practice that Schwend- 

 ler's double-balance method involves all the necessary con- 

 ditions to bring duplex telegraphy on a par with single teleg- 

 raphy. Proceedings Asiatic Society of Bengal, Feb., 1875. 



NEW ELECTRIC APPARATUS FOR RAILROADS. 



Preece's single-wire block signaling instruments are in ex- 

 tensive use in England. They possess one special and im- 

 portant advantage which no other single-wire system has : 

 that the consentaneous action of the two signal-men at the 

 station in advance and in the rear is necessary in order to 

 lower the semaphore to the point which indicates " all 

 clear," thus avoiding the production of a false safety signal 

 from any accidental current. A part of the same apparatus 

 consists in the single repeater which repeats back electrically 

 the movements of a signal which may be out of sight of the 

 man who works it. Forty-second Ann. Rep. of the Royal 

 Cornwall Polytechnic Society, 80. 



EAST INDIAN TELEGRAPHY. 



The reports from the Indo-European Telegraph Company 

 say that the average time in transit between London and In- 

 dia, via Teheran, of all outward messages to India, including 

 the messages for Penang, Singapore, China, Japan, Java, and 

 Australia, for the week ending October 8th, was one hour 

 and sixteen minutes. Engineer, XL., No. 1034, 281. 



ATMOSPHERIC ELECTRICITY. 



Professor Van der Mensbrugghe, in a memoir on the ap- 

 plication of thermo-dynamics to the study of the variations 



