Journal - Franklin Institute of the State of Pennsylvania (1826)
Franklin Institute, Philadelphia, Franklin Institute (Philadelphia, Pa.) · [Philadelphia : Franklin Institute] · leaf 494
s duplex-bi-polar telephone. The object of this instrument is to increase thevolume and clearness of the sound. This he endeavored to secure bythe combination with a common mouth-piece, of a series of diaphragmswith their corresponding magnets arranged in pairs on the outer,opposite sides of the… … Fig. 7.—Grays Duplex-Bl-polar Telephoue. Gray has produced a number of modifications of his bi-polarinstrument. Besides the duplex bi-polar telephone above described,he patented, in 1878, another modification intended to increasethe electro-motive force of the generated current, and to obtainan…
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