168 ANNUAL RECOKD OF SCIENCE AND INDUSTRY. 



discharge formed at the negative pole shows these fine lines 

 only in the immediate neighborhood of the pole, and has no 

 isolated branches. It will be remembered that the figures 

 called Lichtenberg figures show also a very remarkable dif- 

 ference between the two electricities. The most instructive 

 peculiarity of Schneebeli's figures is found in a very well- 

 marked point near the centre of the figure, and separating 

 the positive from the negative discharge. This central point 

 has every appearance of being that in which the layers of air 

 meet, after moving in opposite directions from either pole to- 

 ward the centre. When very strong electric discharges are 

 employed, this peculiar meeting-point is obscured, but becomes 

 very distinctly marked when feebler discharges are made. 

 Bulletin Soc. cles Sciences JVaturelles, JVeuchatel^ -^^<^% 1875. 



DUPLEX TELEGRAPHY. 



In some historical notes on the development of duplex 

 telegraphy, Mr. Cracknell, the superintendent of electric 

 telegraphs in New South Wales, states that this art, which 

 consists essentially in working in two opposite directions on 

 one wire simultaneously, was first tried as far back as in 

 1853, by Dr. Gintel, the director-general of telegraphs in 

 Austria, on the line from Vienna to Prague. In his arrange- 

 ment the compensating currents of electricity could not well 

 be controlled, and the system was not found to be a practi- 

 cal success, although experimentally it worked beautifully. 

 In 1854 Frecher, Siemens, and Halske devised a modification 

 of the duplex method by adopting a somewhat complicated 

 system of resistance coils. These were the first Morse in- 

 struments used on telegraph lines in New South Wales, in 

 January, 1858. They could not be made to work satisfac- 

 torily, and were reduced to single-acting Miller's recorders. 

 Siemens and Halske's arrano-ement was worked on what is 

 called the diff*erential principle. Stearns' duplex system, 

 lately perfected in America, and now attracting the attention 

 of telegraph engineers in most parts of the world, is on a 

 principle which is dependent on producing an equality of 

 tensions, which are sometimes called potentials. With tliis 

 system the relay coils are wound with double wires. It has 

 proved a great success, partly by improvements on old 

 principles, but more particularly in consequence of the intro- 



