ricr. i- 



Fij. 



.a.. 



-c^^J 



r*- 



'^ 



■ — ^r 



E 



3 















_, — ■ ti;ii 





-3 



ft 1 



Fiq. 3. 



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Figure 78. — Patent drawings of Watson's 

 polarized ringer. From U.S. patent 210886 

 (December 17, 1878). 



earlier claims to priority made by Bell and by Edi- 

 son.^'' In 1903 the United States Supreme Court 

 finally declared the Berliner patent valid but restrict- 

 ed the claims of this patent to metal electrodes.^* In 

 its 1903 ruling the Supreme Court decreed that 

 Berliner's patent application disclosed invention but 

 added nothing of practical value to the telephone. 

 Because Berliner's patent was limited to the use of 

 metal electrodes, it did not infringe on the use of 

 carbon transmitters in telephones. Edison's claims 

 to priority in the invention of the carbon trans- 

 mitter were maintained throughout the lengthly 

 litigation concerning telephone transmitter patents. 

 However, by the end of the legal battle, the American 

 patent rights on his transmitter were lost because his 

 European patents had expired. When a European 

 patent had expired, its American counterpart was 

 also invalid. 



But long before the courts had reached these deci- 

 sions, commercially successful carbon transmitters had 

 been invented and placed in operation. The first of 



these (figs. 74, 75) was designed by Francis Blake ^' 

 early in 1878. In Blake's transmitter a platinum 

 bead was fastened to the back of the diaphragm, and 

 the diaphragm pushed the bead against a carbon 

 block. Blake offered his transmitter to the Bell Com- 

 pany, and it was promptly purchased. At first this 

 transmitter gave quite a bit of trouble until Berliner 

 showed how a harder carbon block would improve it. 

 This modification made it a more sensitive instrument 

 than Edison's transmitter and capable of providing a 

 more powerful signal than either the Bell or Edison 

 device. After Blake's instrument was patented in 

 England on January 20, 1879, and in the United 

 States on November 29, 1881, it was used extensively 

 for some years by the Bell Company as standard 

 equipment. 



The next steps in the development of the modulat- 

 ing transmitter were i^rought about by two inventors 

 who made some changes in the shape and size of the 

 carbon electrodes. An English clergyman named 

 Henry Hunnings ^^ replaced the single piece of carbon 

 used in the Blake instrument by granules of coke. 

 These granules were placed between the diaphragm 

 and a metal back. Hunnings' English patent was 

 issued September 16, 1878, and the American patent 

 (fig. 76) was issued in 1881 to the American Bell 

 Telephone Company. The Hunnings transmitter was 

 quite efficient. It had the quality of Blake's trans- 

 mitter but could carry more current than the Blake 

 instrument. In 1886 Edison improved the Hunnings 

 device by substituting granules of anthracite coal for 

 the coke. This improvement fell within the claims of 

 one of Edison's early patents on the carbon trans- 

 former, and he modified this patent accordingly. 



The weakness of the granular carbon transmitter 

 was that, with use, a packing of the granules occurred 

 resulting in a loss of sensitivity. This problem was 

 solved by replacing the metal back by a solid block of 

 carbon. This improved device (fig. 77), patented by 

 A. C. White on November 1, 1892 (U.S. patent 

 485311), is essentially the same as our present carbon 

 transmitter. 



In the meantime the Bell Company had consoli- 

 dated its rights to the monopoly of the telephone 

 business. In 1878 the American Bell Telephone Com- 



^T Federal Reporter, 1895, vol. 65, pp. 86-91; 1895, vol. 68, 

 pp. 542-570; 1901, vol. 109, pp. 976-1056. 

 58 Federal Reporter, 1903, vol. 119, pp. 893-917. 



5» Francis Blake, U.S. patents 250126-250129 (November 

 29, 1881); British patent 229 (January 20, 1879). 



6" Henry Hunnings, British patent 3647 (September 16, 

 1878); U.S. patents 246512 (.August 30, 1881) and 250250 

 (November 29, 1881). 



330 



BULLETIN 228: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



