456 RIESS ON THE INCANDESCENCE OF 
varies with the kind of metal of which the wire is composed. 
Although with platina and palladium the quantity has been 
found to be considerable, with copper it is found to be less, with 
silver and iron still less, and with brass and German silver ex- 
tremely small. With wires of the two last-named metals it 
therefore frequently happens that the quantity of electricity 
which produces in them the first distinct appearance of incan- 
descence, upon being discharged a second time through the wire 
causes them to break. Even with new wires of brass and Ger- 
man silver, when the quantity of electricity discharged through 
them was increased ,\,, instead of producing the first signs of 
incandescence it broke them asunder. 
The shivering to pieces. 
If wires are exposed to stronger discharges than such as are 
necessary to break them, a flash of light appears, and they are 
shivered into a greater or lesser number of pieces, which are 
scattered about to some distance. It is perceptible on the exa- 
mination of the collected fragments that the division of the wire 
into small pieces is caused by a slitting and shivering action, 
and that fusion, where it has taken place, is a secondary phz- 
nomenon. I shall select from my experiments upon this subject 
chiefly those from which the pieces of wire have been preserved, 
and can therefore be subjected to further examination. 
Experiment 28.—A platina wire, 0°076 line thick, 16 lines 
long, was surrounded by a glass tube 7} lines in diameter and 
fixed in the connecting circuit. The discharge of the quantity 
of electricity 22 contained in seven jars, just produced incandes- 
cence in the wire; the quantity of electricity 35 scattered it in 
pieces, which were found in the glass tube. These fragments 
bore evident marks of fusion on their surfaces, and four of the 
largest of them appeared soldered together, forming an entangled 
figure, which led to the supposition that they must, whilst hot, 
have been forcibly ejected against each other and against the 
sides of the tube. But the ends of all the pieces were not fused ; 
at first sight most of them appeared sharply pointed. A tolerably 
straight fragment was placed under the microscope; its surface 
appeared uneven. On measuring its diameter with the screw- 
micrometer, it was found in the middle to be 0-081 line, 
0:083 
at one end 0:022_... 
0:029 
