METALLIC WIRES BY ELECTRICITY. 453 
the incandescence of another wire. Thus, let the thermometri- 
cal indication, radius, and relative power of the current be, 
For the first wire . . 6 r 4, 
For the second wire . 4 7 7, 
the relation existing will be 
yl \4 
g = -(“) 6. 
AW 
If, for example, in the connecting circuit an electrical ther- 
mometer sink 25°5 degrees, whilst at another part of the circuit 
a German silver wire of 7 lines radius is made incandescent by 
the discharge, then if a copper wire of 7” lines radius is to be 
. 1,4 
made incandescent, the thermometer must sink a 25°5 (I 
degrees. 
Although, from the nature of the experiments, no very great 
degree of accuracy can be ascribed to the numbers in the table 
above, still it is evident that they depend upon the power pos- 
sessed by the wires of retarding electricity, and in general in- 
crease as this decreases. In addition to this, the capacity for 
heat and the specific weight of the wires exert some influence, 
which however is by no means apparent, according to the laws 
which I established for the excitation of heat alone*. If this 
indeed were the case, then the power of the current, multiplied 
by the retarding power and divided by the product of the capa- 
city for heat multiplied by the specific weight, would give nearly 
the same quotient for every metal, which does not result. 
Besides those named there are other properties of the metals 
which affect their incandescence, and which cannot be subjected 
to calculation. These are, probably, brittleness and the facility 
with which the metal combines with the oxygen of the air. [The 
more easily oxidizable metals, as iron, brass and copper, become 
tarnished of various colours before their incandescence.] The 
numbers in the series above can therefore only be valid for con- 
stant quantities, which must be determined empirically. 
PH#NOMENA WHICH FOLLOW INCANDESCENCE. 
Breakage. 
A platina wire, 0°0209 line in radius and 10 lines long, was 
laid in the discharger and exposed to increasing discharges. 
* Poggendorff’s Annalen, vol. xlv. p. 28. 
