WIRELESS TRANSMISSION OF ENERGY. 



By Elihu Thomson. 



It will be my purpose in the present discourse to outline the gen- 

 eral nature of wireless transmission and to indicate its relationship 

 to transmission by wire. It will also be my object to show why the 

 wireless energy sent out follows the curvature of the earth and to 

 explain other features which to many have been more or less puz- 

 zling. In short. I desire to present in simple terms a view of the 

 nature of such wireless work, so that anyone reasonably informed 

 about electrical actions can obtain, as it were, a mental picture of 

 the process. I may here state the fact that perhaps one of the earli- 

 est experiments bearing on wireless transmission was made in com- 

 pany with Prof. E. J. Houston, Avhile we were both teachers in the 

 Central High School in Philadelphia. This old experiment to 

 which I refer was made about the latter part of 1875, and briefly 

 described in the Franklin Institute Journal early in 1876. It con- 

 sisted in using an induction coil which would give a spark length of 

 several inches, then known as a Ruhmkorff coil, the coil resting on 

 the lecture table, one terminal of the fine wire or secondary of which 

 w^as connected to a water-pipe ground, while the other was con- 

 nected by a wire 4 or 5 feet long to a large tin vessel supported on a 

 tall glass jar, insulating the tin vessel from the lecture table. The 

 coil had an automatic interrupter for the primary circuit, and when 

 in operation the terminals of the secondary were approached so that 

 a torrent of white sparks bridged the interval between them, the 

 gap being about 2 inches or so in length. Figure 1 shows this 

 iirrangement. When the coil was worked in this way. it was found 

 that a finely sharpened lead pencil approached to incipient contact 

 Avith any metallic object — such as door knobs within the room and 

 outside thereof — would cause a tiny spark to appear at the incipient 

 contact between the pencil point and the metal. This, of course,, 

 was not a very delicate detector, but was improved, as in figure 2, 

 by putting two sharpened points in a dark box, a device due to 



1 Lecture by Prof. Thomson, printed after revision by tbe author, by permission of the 

 National Electric Light Association, New York, 



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