298 Mr McClelland, On the Action of Incandescent Metals 



the cylinder G between two thick copper wires G and G' which 

 pass through ebonite plugs at F and F\ The wires G and G' are 

 connected to the terminals of a battery B of a few large storage 

 cells through a rheostat R, so that any required current can be 

 used to heat the wire W to the desired temperature. The battery 

 B and rheostat R are placed on blocks of paraffin so that the 

 whole circuit in connection with the wire W can be insulated. A 



Fig. l. 



second battery of a large number of small storage cells is used to 

 raise this circuit to any required potential. One point of the 

 battery of small cells is put to earth and another point connected 

 to the circuit containing the wire W, so that W is heated by the 

 current from B and at the same time is raised to any potential 

 required. The potential difference between the ends of W is very 

 small compared with its mean potential. The cylinder C is con- 

 nected to one pair of quadrants of an electrometer, the other pair 

 of quadrants being permanently to earth. The quadrants con- 

 nected to C are first earthed, then insulated and the time observed 

 until G, with whatever capacity is connected to it, is charged to 

 some definite potential. This gives a measure of the current 

 through the gas between the charged wire W and the cylinder C. 



