8 C. A. Chant — Variation of Potential along the 



Inductive Method of Excitation (JBraun, Marconi). 

 The experimental disposition used for inductively exciting 

 the oscillations about the antenna is illustrated in fig. 4. 



Cj, C 2 are two condensers. From the inner coatings con- 

 ductors lead off and end in knobs, between which sparks are 

 made to pass by an induction coil. The outer coatings are 

 joined by a thick wire bent into a single turn which acts as the 

 primary of a transformer. The secondary of this transformer, 

 AB, consists of a few turns. To one end of it, A, the antenna 

 is joined and to the other end, B, the earth, any desired capac- 

 ity or a wire similar to the antenna. 



The apparatus actually used in the investigation was the 

 transmitter of the experimental set supplied by the Gesell- 

 schaft fur drahtlose Telegraphie, Berlin, Germany, of the sys- 

 tem Prof. Braun and Siemens & Halske. Each condenser 

 consisted of four small tubular jars, 17"5 mm in diam., 2 mm thick 

 and with coatings approximately 7'5 cras high. The spark-gap 

 was from 1 to 2 mm long, and no attention was paid to polishing 

 the knobs. That portion of the condenser circuit forming the 

 primary of the transformer was a single turn of copper wire 

 6 mm in diameter, bent into a circle of mean diameter 6-8 cms 

 (D, D, fig. 5). The secondary, which was within the primary, 

 consisted of 5-J- turns of heavily insulated wire of a total 

 length of 99 cms . The diameter of the wire and its insulation 

 was 2*5 mm , and the turns lay close together. A vertical sec 

 tion, one-half of full size, is shown in fig. 5. 



