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THE POPULAR SCIENCE MONTHLY 



The mouth-tube communicates with the inside of the box or air- 

 chamber, and the sound-waves act upon the tympanum from beloAV. 

 On the side of the box are seen a telegraph key, e, and sounder, for sig- 

 nalizing between the transmitting and receiving stations. This is the 

 transmitter successfully used, as will be seen, by Yeates, in Dublin, 

 in 1865. So sensitive was this transmitter that it was found unneces- 

 sary, in its early use, to speak directly into the mouth-piece ; and in 

 practice the speaker talked and sang at a little distance from it. In 

 the reports of experiments with this instrument the rattling noises 

 which were sometimes complained of as heard in the receiver were 

 undoubtedly due to the complete breaking of the circuit by too loud 

 talking or singing in the mouth-piece. The Berliner and Blake trans- 

 mitters are liable, unless specially guarded, to the same misadventure 

 from the same cause. 



The receiver in Fig. 2 is Reis's latest form of the " knitting-needle " 

 instrument. A helix of insulated wire is attached horizontally to a 

 sounding-box. Through the helix a steel wire or knitting-needle is 

 passed without contact, and supported at each end by a bridge. The 

 vibrations of this knitting-needle magnet, corresponding exactly to 

 the vibrations of the tympanum of the transmitter, are converted into 

 sound-waves by the extended surface of the box acting upon the air. 

 On the side of the box is a telegraph-key to communicate back to the 

 transmittei'. The code of signals suggested in the accompanying 

 "Prospectus" contains the following : 



" One tap = sing. 

 Two taps = speak." 



An original telegraphic letter alphabet is also suggested, showing 

 how slight was Reis's acquaintance with ordinary telegraphing. 



Fig. 3. 



Fig. 3 represents the form of transmitter, figured and described by 

 Reis in his first memoir of 1861. I present it, out of chronological 

 order, on account of its simplicity and close resemblance to the mod- 

 ern transmitters. A conical chamber, a b, is bored through a cubical 



