HERTZIAN WAVE WIRELESS TELEGRAPHY. 445 



In the discussion which followed the reading of this paper, Pro- 

 fessor ]\Iinchin described the effects of electric radiation on his im- 

 pulsion cells. He followed up this by reading a paper to the Physical 

 Society on November 24, 1893, on the action of Hertzian radiation on 

 films containing metallic powders, and expressed the opinion that the 

 change in resistance of the Branly tube was due to electric radiation.* 



Thus, at the end of 1893, a few physicists clearly recognized that a 

 new means had been given to us for detecting those invisible ether 

 waves, the chief properties of which Hertz had unraveled with sur- 

 passing skill six years before, by means of a detecter consisting of a 

 ring of wire having a small spark gap in it. 



In June, 1894, Sir Oliver Lodge delivered a discourse at the Eoyal 

 Institution, entitled 'The Work of Hertz,' and at this lecture use was 

 made of the Branly tube as a Hertz wave detecter. The chief object 

 of the lecture was to describe the properties of Hertzian waves and their 

 reflection, absorption and transmission, and many brilliant quasi- 

 optical experiments were exhibited. Although a Branly tube, or im- 

 perfect metallic contact, then named by him a coherer, was employed by 

 Sir Oliver Lodge to detect an electric wave generated in another room, 

 there was no mention in this lecture of any use of the instrument for 

 telegraphic purposes, f 



As we are here concerned only with the applications in telegraphy, 

 we shall not spend any more time discussing the purely scientific work 

 done with laboratory forms of this wave detector. 



Without attempting to touch the very delicate question as to the 

 precise point at which laboratory research passed into technical applica- 

 tion, we shall briefly describe the forms of kumascope which have been 

 devised with special reference to Hertzian wave telegraphic work. A 

 very exact classification is at present impossible, but we may say that 

 telegraphic kumascopes may be roughly divided into six classes. The 

 first class includes all those that depend for their action on the ' coherer 

 principle' or the reduction of the resistance of a metallic microphone 

 by the action of electromotive force. As they depend upon an im- 

 perfect contact, they may be called contact humascopes. This class is 

 furthermore subdivided into the self-restoring and the non-self-restor- 

 ing varieties. The second class comprises the magnetic kumascopes 



* See Professor Minchin, Proc. Phys. Soc, November 24, 1893; or The 

 Electrician, Vol. XXXII., 1893, p. 123. See also Professor Minehin, Phil. Mag., 

 January, 1894, Vol. 37, p. 90, ' On the Action of Electromagnetic Radiation on 

 Films containing Metallic Powders.' 



t This lecture was afterwards published as a book, the first edition bearing 

 the same title as the lecture, viz., ' Tlie Work of Hertz and Some of his Suc- 

 cessors.' In the second edition, published in 1898, an appendix was added (p. 

 59) containing 'The History of the Coherer Principle,' and the original title 

 of the work had prefixed to it, ' Signalling without Wires.' 



