DEVELOPMENT OF TELEPHONE SERVICE 



407 



the United States Coast Survey, and during the next three years 

 assisted in the transcontinental longitudinal determinations. Finding 

 it necessary to make many experiments in determining the velocity 

 of telegraphic time signals over long circuits, he made a thorough 

 study of electricity. In 1869 and again in 1872 he was in Europe 

 and made all the observations in the third and final determination of 

 the difference of longitude between Greenwich, Paris and Cambridge. 

 Subsequent observations by European astronomers confirmed his work. 

 During 1874—6, he was preparing the results of his transatlantic 

 work for publication, and during this period became acquainted with 

 Graham Bell. On April 5, 1878, he tendered his resignation, which 

 was accepted with the greatest reluctance to date April 15. During 

 the four years that had elapsed since his return from Europe he had 

 devoted all his leisure to experimental physics. It is recorded that 

 in carrying on these experiments 



he had become an enthusiastic amateur mechanic; so that at the time of his 

 resignation he found himself in possession of a well-equipped mechanical labora- 

 tory, and a self-acquired ability to perform a variety of mechanical operations. 

 Under these conditions what had been a pastime naturally became a serious 

 pursuit in life; and within barely a month of his resignation, April 5, 1878, 

 Mr. Blake had begun a series of experiments which brought forth the Blake 

 transmitter. 



Other workers were also 



successful in serviceably util- 

 izing the ' loose contact ' or 

 microphonic principle in the 

 telephonic transmitter. In 

 January, 1877, Emile Berliner 

 devised his well-known trans- 

 mitter, for which he filed a 

 caveat on April 14. It was 

 referred to in the Washington 

 Critic, May 18, and on June 

 4, 1877, he filed an applica- 

 tion based on his caveat. The 

 patent was issued January 15, 

 1878. On April 27, 1877, 

 Thomas A. Edison filed his application for a patent on a battery trans- 

 mitter; while in December, 1877, Professor Hughes commenced his 

 now famous microphonic experiments, which were followed by Hun- 

 nings's employment of carbon granules. One of the first of the Ber- 

 liner transmitters is illustrated in Fig. 32 



Beferring to some of these experiments with carbon electrodes, Sir 

 William Thomson (now Lord Kelvin) wrote: 



fig. 32. 



