. An elementary manual of radiotelegraphy and radiotelephony for students and operators . ter conductivity, and the current from thecell passes through the mass and deflects the galvanometer. Branlyfound the same effect takes place when a loose or imperfect contactis formed bstween two pieses of slightly oxidised metal, such ascopper or steel wires, and he found that this contact drops inresistance from many thousands of ohms to a few ohms under theinfluence of an electric spark made some yards away. He alsonoted that a slight tap or blow destroyed the improved contact. These observations did
. An elementary manual of radiotelegraphy and radiotelephony for students and operators . ter conductivity, and the current from thecell passes through the mass and deflects the galvanometer. Branlyfound the same effect takes place when a loose or imperfect contactis formed bstween two pieses of slightly oxidised metal, such ascopper or steel wires, and he found that this contact drops inresistance from many thousands of ohms to a few ohms under theinfluence of an electric spark made some yards away. He alsonoted that a slight tap or blow destroyed the improved contact. These observations did not attract attention in England untildescribed by Dawson Turner, in 1892, and they were then re-peated by Croft before the Physical Society, in 1893, and carefullyexamined by Minchin and Lodge in the same year. In 1894,Lodge made use of a tube of glass full of loosely aggregated ironor brass filings contained between two plugs to detect the existenceof electric ■s\aves created by a spark discharge. He christenedthis device a coher&r, because he considered that the action of the. Fig. 2. OS C ILL A TION DE TEC TORS 197 oscillations produced by tlio iucidout electric wave was to maketho parlieUiS eoheiij together. A similar typo of dottctor was employed by PopufTin Russia inresearches on atmospheric electricity, ami described by him at thebej^inning of 18JG. In the same year (5. Marconi described in uHritish Iatcnt Spi-citication a (^rtatly imi>ro\ed form of metallictilings oscillation detector constructeil in tho fullowiiig nianner:—In a small glass tul)e about 3 or 4 cms. long and 5 diameter, he placed two silver plugs fitting the tubetightly. To these plugs were attached platinum wires sealedthrough the closed emls of a tube. The inner ends of the plugswere polisheil and slightly amalgamated with mercury and broughtwithin a couple of millimetres of each other. The interspace wastilled with a very small quantity of nickel and silver filings, 95 percent, nic
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1916
