120 Trans. Acad. Sci. of St. Louis. 



that the dynamo and motor were complementary, but the 

 reversibility of the Gramme dynamo as shown at the Vienna 

 Exposition of 1873, and repeated at the Centennial Exposition 

 at Philadelphia in 1876 was a most impressive lesson to all who 

 saw it. Nevertheless it was not until 1880 that the scientific 

 world was ready to admit that an enormous development of 

 electrical industries was possible. It was then that the ques- 

 tions of economy were settled which showed the great eco- 

 nomic advantage of the dynamo and the steam engine over 

 the primary battery, and that large electrical plants with 

 their high efficiency were possible. 



The first telephone was constructed and operated by Philipp 

 Reis in 1861 and 1862, and he gave his instrument the name 

 telephone. His system consisted of a transmitter or loose 

 contact which was disturbed by a membrane put into vibra- 

 tion by the sound wave, a receiving instrument consisting of 

 an electromagnet or sounder upon a sounding board, and a 

 battery. This is broadly, so far as it goes, a complete descrip- 

 tion of the telephone of to-day. 



Bell modified the Reis receiver, making the armature in the 

 form of an iron disc, and used the same instrument for a trans- 

 mitter. In Bell's system, the sound waves were the source 

 of power for setting the armature into vibration, such vibra- 

 tion by a dynamo action producing currents having the char- 

 acteristics of the sound waves. In the Reis system the power 

 was supplied by a battery, the current being moulded by the 

 voice acting upon the loose contact in the transmitter. 



The Reis instrument did not prove practical because the 

 materials used were not the best that could be chosen. The 

 membrane of his transmitter was of animal tissue, while iron 

 is now used, and the loose contact was between platinum 

 points, while carbon is now used. The Reis receiver was not 

 sensitive enough. 



The Bell system failed because the receiving instrument 

 was not adapted to use as a transmitter, although his re- 

 ceiver was a great improvement upon that of Reis. The tele- 

 phone of to-day is the improved Reis telephone. It is coming 

 into more general use in the country than in the cities. In 

 the great farming region of the upper Mississippi valley the 



