212 Messrs. Trowbridge and Duane on 



e> 



used so successfully by Blondlot. The first attempt arranged 

 on the electrostatic principle proved a complete failure. A 

 second trial about a fortnight later, however, was so successful 

 that we fully determined to adopt the electrostatic method. 



The first point in the course of the investigation worth 

 detailed description is the production of electric waves along- 

 parallel wires in such a manner that they are actually visible 

 to the eye. The arrangement of the apparatus to accomplish 

 this was as follows : — 



Fig. l. 



E 



B 

 T J 



H L 



A primary condenser AB (fig. 1) was held with its plates 

 in vertical planes by means of suitable wooden supports (not 

 represented in the figure), and was joined in a circuit BO 

 consisting of two wires about 75 centim. long placed 4 centim. 

 apart. In reality this circuit BC should be represented as 

 perpendicular to the plane of the paper (which is taken as the 

 horizontal plane passing through the centre of the apparatus). 

 The plates of the condenser AB were sheets of tinfoil 

 101 X 40 centim. glued to hard-rubber sheets, and the dielectric 

 between them consisted of other similar sheets of hard rubber 

 sufficient in number and thickness to make the distance 

 between the condenser plates 4 # 2 centim. Outside the primary 

 condenser plates and separated from them by hard-rubber 

 plates (total thickness '6 centim.) were two secondary plates, 

 E and F, each 40 centim. square. To these plates was 

 attached the secondary circuit EGJHF, the form of which is 

 represented in the figure. This latter circuit consisted of 

 copper wire, diameter *13 centim., and its total length from 

 E to F was 4200 centim. A spark-gap with spherical 

 terminals 2'5 centim. in diameter was placed at C in the 

 primary circuit, and another spark-gap with pointed terminals 

 was sometimes inserted at J in the secondary circuit, although 

 this latter spark-gap had no effect upon the phenomena to be 

 described. The primary condenser was charged by means of 

 a large Ruhmkorf coil excited by five storage-cells with a total 

 voltage of ten volts. The current from these cells was made 

 and broken by the automatic interrupter used by Mr. St. 

 John and described by him in his paper above referred to. 



