. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. SIGNALING THROUGH SPACE WITHOUT WIRES. 251 In the first case the charges can be made to rise and fall, and to surge to and fro with rhythmic regularity, exciting electric waves along each line of electric force at very high frequencies, and in the second case the currents can rise or alternate in direction with the same regu- larity, but with very different frequencies, and originate electromag- netic waves whose wave fronts are propagated
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. SIGNALING THROUGH SPACE WITHOUT WIRES. 251 In the first case the charges can be made to rise and fall, and to surge to and fro with rhythmic regularity, exciting electric waves along each line of electric force at very high frequencies, and in the second case the currents can rise or alternate in direction with the same regu- larity, but with very different frequencies, and originate electromag- netic waves whose wave fronts are propagated in the same direction. The first is the method of Hertz, which has recently been turned to practical account by Mr, Marconi, and the second is the method which I have been applying, and which, for historical reasons, I will describe to you first. In 1884 messages sent through insulated wires buried in iron pipes in the streets of London were read upon telephone circuits erected on poles above the house tops, 80 feet away. Ordinary telegraph circuits were found in 1885 to produce disturbances 2,000 feet away. Distinct speech by telephone was carried on through one-quarter of a mile, a CURRENT BREAKER Fig. 1.—Diagram of connections of Mr. Preece'a system. distance that was increased to 1£ miles at a later date. Careful experi- ments were made in 1880 and 1887 to prove that these effects were due to pure electromagnetic waves, and were entirely free from any-earth- conduction. In 1892 distinct messages were sent across a portion of the Bristol Channel, between Penarth and Flat Holm, a distance of miles. Early in 1895 the cable between Oban and the Isle of Mull broke down, and as no ship was available for repairing and restoring com- munication, communication was established by utilizing parallel wires on each side of the channel and transmitting signals across the space by these electromagnetic waves. The apparatus (fig. 1) connected to each wire consists of— (a) A
Size: 2141px × 1167px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorsmithsonianinstitutio, bookcentury1800, bookdecade1840
