METALLIC WIRES BY ELECTRICITY. 447 
brevity, therefore, we shall measure the current by its heating 
power, and always understand by the expression, Power of the 
current of discharge, the amount of heat which it is capable of 
producing in a wire of constant dimensions forming part of the 
connecting circuit. 
The contents of this paragraph may therefore be thus ex- 
pressed: Whenever a wire forming part of the connecting circuit 
of a battery is made incandescent by the discharge, the same 
takes place, whatever changes may be made in the number of 
jars or in the quantity of electricity, provided the power of the 
current of discharge remain unchanged. 
Incandescence of a Wi-e according to its Length. 
In experiment 9, a platina wire of 26°6 lines in length was 
made incandescent by a current of discharge, the mean power 
of which was 20°8 ; in experiment 10, a wire was made incan- 
descent by a current of 20-4; and in experiment 11, when the 
length of the wire was 10°7 lines, the power of the current was 
found to be 20°3. I took a similar wire, 49°5 lines long, and 
found that it became incandescent when the thermometer indi- 
cated a current of 20°8. In these experiments with wires ot 
different lengths, therefore, very nearly the same power of cur- 
rent was observed. 
Experiment 12.—A platina wire 15°7 lines long, became in- 
candescent with— 
Number Quantity Power of 
of jars. of electricity. discharge. 
4 12 83 
12 8°0 
7 15 es 
Experiment 13.—A similar wire, 77°5 lines long, to be brought 
to an incandescent state, required— 
Number Quantity Power of 
ofjars. of electricity. discharge. 
4 22 8°3 
22 8°0 
22 8:0 
A wire therefore 15:7 lines in length was made incandescent by 
a current 8°0, and one 77°5 lines in length by a current of the 
same power, although in the latter case a much larger quantity 
of electricity was discharged than in the former. From this it 
