298 Mr McClelland, On the Action of Incandescent Metals 
the cylinder C 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 
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 C, 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. 
