. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. TELEGRAPHY OF PHOTOGRAPHS BAKEE, 263 prism inside the cjdinder on to the selenium cell, throngh which the current passes. Across the circuit is shunted a galvanometer of the Einthoven pattern, containing two fine silver strings free to move laterally in a strong magnetic field. These are represented by AB, the magnet poles being MM. When a bright part of the photograph admits of light falling on the sensitive cell, current passes through AB
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. TELEGRAPHY OF PHOTOGRAPHS BAKEE, 263 prism inside the cjdinder on to the selenium cell, throngh which the current passes. Across the circuit is shunted a galvanometer of the Einthoven pattern, containing two fine silver strings free to move laterally in a strong magnetic field. These are represented by AB, the magnet poles being MM. When a bright part of the photograph admits of light falling on the sensitive cell, current passes through AB, and it shifts aside, allowing light from a Nernst lamp No to enter the prism P, whence it is reflected on to the second cell SS. The tele- phone lines connecting the two instruments go direct to the wires of a similar galvanometer, which is in series with the galvanometer of the transmitting instrument. If w^e imagine MM to be the receiving galvanometer, then we remove the prism P, and the light acts on a sensitive photographic film attached to the drum C, which revolves synchronously with the glass cylinder of the sending instrument. The inertia of selenium once overcome, the metal immediately be- comes of great use for many purposes. Prof. Korn's method of com-. FiG. 2. pensation is to let the light fall at the same time on two cells of op- posite characteristics; one has great inertia and small sensitiveness, the other low inertia and great sensitiveness. By using the two cells on opposite sides of a AVlieatstone bridge, dividing the battery into two parts for the other sides, the deflection in the galvanometer is very rapid. You will see the effect from the two curves now shown on the screen. That above the axis along which exposure is measured is the sensitive cell; that below this axis the cell of low sensitiveness. Clearly the current passed through the galvanometer is that obtained by joining the sums of the ordinates. This gives the small curve shown as the shaded po
Size: 2420px × 1032px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorsmithsonianinstitutio, bookcentury1800, bookdecade1840
