60 Messrs. Boys, Briscoe, and Watson on the 



scale. The ends of the wire were brought out at the bottom 

 of the tube, leaving about half an inch free. When using a 

 continuous current, two brass clips (A, fig. 11) were placed 

 on these ends so as to connect them to a pair of binding- screws. 

 When using the oscillator these clips were turned down (as 

 in the figure), so that the wire should not be connected with 

 any body having capacity. 



The following are the dimensions of this tube (No. 4) : — 



Length 126 centimetres, diameter 4*7 centimetres. 



Length- of wire 2 x 103 centimetres. 



Resistance of wire 38 ohms. 



Diameter of guard-tube 7 centimetres. 



Diameter of mirror 1*2 centimetre. 



Length of fibre 9 centimetres. 



As shaking interfered with the working of the instrument, 

 the experiments were performed in a vault, which, however, 

 was by no means steady. 



The following are the results obtained when testing the 

 sensibility of the instrument (scale at 100 centimetres from 

 mirror) : — 



Added Eesistance. 



Total Eesistance. 



Deflexion. 



ohms. 

 500 



762 



ohms. 

 538 



800 



centimetres. 

 33 



1-6 



In the case of 800 ohms total resistance we have 

 Heat developed in wire per sec. — -7=72 x t^ 



= '000,014 calorie. 



This is equivalent to one calorie developed in 19 hrs. 42 min. 

 Or we may say that one calorie per day developed by the whole 

 wire could certainly be detected ; that is, one calorie in 

 103 days per centimetre of tube. 



The oscillator used to set up the electromagnetic radiation 

 consisted of two hollow brass cylinders (D E, fig. 11), 

 fixed to ebonite cross pieces (F, C), which could be placed at 

 different heights in a wooden stand. Short brass cylinders, 

 with well-rounded ends, fitted into the ends of D and E, and 

 allowed the length and sparking-distance to be altered. These 

 cylinders were connected by very fine wire with the terminals 

 of the large Ruhmkorff's coil belonging to the Physical 



