WIRELESS TELEGRAPHY FESSENDEN. 167 



mer months or in the Tropics. Roughly speaking, a coherer acts by 

 starting an arc and making a short circuit on the line every time a 

 signal is received, which short circuit persists until it is broken by a 

 blow from an additional mechanism, and such a method of operation 

 is obviously far from practical. In addition, it is practically impos- 

 sible to obtain sharp tuning in a local circuit containing a coherer; 

 its action is always more or less erratic, its electrostatic capacity vari- 

 able, and it is insensitive. 



At the sending end the energy Avhich can be liberated by the dis- 

 charge of an antenna is limited, and in the form used prior to 1897 

 the dampening is so great that there are only a few oscillations per 

 spark. 



Lodge," by placing a coil of large inductance in the antenna, 

 throttled down the amount of energy radiated per oscillation and so 

 obtained with the same limited amount of energy derived from the 

 charged antenna, an increase in the time of damping. 



Braun '^ patented the method of using a local oscillatory circuit 

 connected to an antenna, the local oscillatory circuit having a much 

 longer period than the natural period of the antenna and of a differ- 

 ent order of magnitude. Such a system, however, does not radiate 

 energy appreciably, and produces a damped wave. 



This dampening and the limited amount of energy obtainable by 

 charging and discharging the antenna operates to prevent sharp tun- 

 ing and working over long distances. 



The coherer is well adapted for working with damped waves, but 

 the coherer-damped wave method can never be developed into a 

 practical telegraph system. It is a question whether the invention of 

 the coherer has not been on the whole a misfortune as tending to 

 lead the development of the art astray into impracticable and futile 

 lines and thereby retarding the development of a really practical 

 system. 



The fact that no coherer-damped wave system could ever be de- 

 veloped into a practically operative telegTaph system, and the fact 

 that it was necessary to return to first principles and initiate a new 

 line of development along engineering rather than laboratory lines 

 was perceived in America in 1898 " and a new method was advised 

 which may be called the sustained oscillation-nonmicrophonic re- 

 ceiver method as opposed to the damped oscillation-coherer method 

 previously used. 



« Lodge, Great Britain patent No. 11575, 1897. 



6 Braun, German patent No. 11578, October 14, 1898. 



<' Electrical World, July 29, August 12, September 16, 1899, and Proceedings 

 American Institute of Electrical Engineers, November, 1899, page 635, and 

 November 20, 1906, page 781. 

 88292— SM 1908 12 



