20 Mr. Harris on the relative powers of various 
the wire in the bulb, the relative degree of heat it evolves is 
made evident by the ascent of the fluid along the graduated 
scale. 
I submitted to experiment, by means of this instrument, the 
following metallic substances ; silver, copper, gold, zinc, 
platinum, iron, tin, lead, alloys of gold and copper, of silver 
and copper, of silver and gold, brass, alloys of tin and lead, 
of tin and zinc, and an alloy of tin and copper. The above- 
named metals were carefully drawn through successive holes 
in a plate of steel until their diameters were the same, and 
in order to insure the transmission of an equal and similar 
explosion through each metal, I adopted the following me- 
thod ; two brass balls of the same dimensions were fixed at 
a given distance from each other, as in Lane's well known 
discharging electrometer ; one of these balls, being insulated, 
was placed in immediate connection with the positive side of 
the battery, whilst the other was connected with the negative 
side, the metal to be examined forming part of the circuit. 
This last connection was effected by means of two fixed 
copper wires, inserted into the balls on each side of the glass 
bulb, and made perfect at the points of junction. When there- 
fore the charge, accumulating in the battery, acquired a suffi- 
cient intensity to pass the given interval, the discharge took 
place through the wire in the bulb, which thus became im- 
mediately the subject of experiment. 
The battery consisted of five jars, each containing five 
square feet of coated surface. They were placed on a metallic 
base communicating with the negative conductor, and were 
charged by means of long copper rods projecting immedi- 
ately from the bottom of each jar. 
