metallic Conductors and their Resistance to Electric Currents. 5 



me in a previous communication*. To these is added a pyrometer, which 

 measures the temperature by the expansion of the platinum wire which is the 

 subject of experiment. It is shown at figs. 1 and 2. The wire w, 5.4 



Fig. 1. Fig. 2. 



inches long, is held above by a clip attached to the binding-screw a, which 

 slides in the piece b, and can be pinched in it at any position. Below, the wire 

 is passed round the cylinder c, and secured in front by a screw. The arbor </, 

 which carries the cylinder, has also an arm d, provided with a sectoral arc e, 

 grooved on the exterior to lodge the silk thread /, attached to its lower extre- 

 mity, and coiled above on the arbor i. This is furnished with a pulley A, on 

 which is wound another thread bearing a counterpoise : it also carries the 

 index n, which plays on a dial divided into sixty parts. It will easily be un- 

 derstood from this, that the counterpoise tends to pull up the arm d, and roll 

 the wire on the cylinder c, but is resisted by its tensile force. If now the wire 



* Transactions E. I. A. vol. xxi., Science, p. 291. 



