AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
The mean values of e X a 7 and r X a 7 are respectively 1711 X 10 8 and 717 X 10 8 , and 
as in Wertiieim’s results, platinum and copper differ in respect to these products from 
the mean values, more than the other metals. I have ascertained, however, that 
there is greater accordance between both e X a 7 and r X a 7 , in the case of the different 
metals, than can be obtained by taking the products of e and r with any other 
power of a. 
The Influence of an Electric Current and of Magnetism on the Torsional 
Rigidity of Metals. 
Wertheim has shown* that the longitudinal elasticity of metals is temporarily 
diminished by the passage of an electric current, independently of the alteration 
which would result from the elevation of temperature produced by the current: he 
has also proved that long-continued magnetization diminishes both temporarily and 
permanently the elasticity of iron and steel, but that if the magnetization be continued 
for only a short time there is no sensible effect. As it seemed desirable to supplement 
these observations by others on the torsional rigidity of metals, a few experiments 
were made with this object. 
Experiment XXIV. 
A copper wire, 8 feet in length and ‘095 centim. in diameter, was suspended for 
observations of the torsional rigidity in the manner previously described. To the 
centre of the flat bar which carried the cylinder was soldered a piece of platinum 
wire, about 3 inches in length and ’05 centim. in diameter; the other extremity of 
this latter wire, which hung vertically downwards, dipped into a mercury cup, so that 
by means of the cup and a silk-covered copper wire soldered to the upper bar, from 
which was suspended the wire under examination, connexion could be made with a 
battery of Grove’s cells, in the circuit of which was placed a Gaugain-Helmholtz’s 
tangent galvanometer; with this galvanometer the current of one Daniell’s cell 
freshly charged with sulphuric acid diluted with seven parts of water and sulphate 
of copper solution, a deflection of 24 - 9° was produced through a resistance of 71 ohm. 
Observations. 
Time of one 
vibration. 
Current. 
Total 
percentage of 
diminution 
of rigidity 
caused by the 
current. 
Percentage 
decrease 
of rigidity 
produced by 
heating effect 
of current. 
Percentage 
decrease 
of rigidity 
caused by the 
current 
proper. 
Platinum wire out of mercury cup 
Seconds. 
5-570 
0 
Platinum in cup. 
5-568 
0 
Wire shortened. 
5-355 
0 
5-395 
73°-4 
1-54 
•63 
•91 
5-361 
0 
1-26 
•63 
•63 
MDCCCLXXXIII. 
* Ann. de Chimie, 1844, tom. xii., p. CIO. 
F 
