THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JUNE 1850. 



LI I. On the Measurement of Temperatures by Thermo-electric 



Currents. By M. Regnault*. 



[With a Plate.] 



IT is known, from the beautiful discovery of Seebeck, that 

 when a closed circuit is formed with two plates of differ- 

 ent metals soldered at their extremities, and that the tempe- 

 rature of one of the junctions is raised, an electric current is 

 formed, which is in general the more intense the greater the 

 difference of temperature at the two places of soldering. Phi- 

 losophers immediately sought to turn this property to ac- 

 count for measuring temperatures. 



As we possess extremely delicate apparatus, by means of 

 which, to a certain point, the weakest currents may be de- 

 tected and measured, while on the other hand the metallic 

 plates forming the circuit may be replaced by wires of very 

 small diameter, exceedingly small thermoscopic apparatus, 

 capable of demonstrating the feeblest variations of temperature, 

 have been constructed. Every one is aware of the advantage 

 which MM. Becquerel and Breschet have derived from these 

 apparatus in measuring the differences of temperature exhi- 

 bited by the several parts of the human body, and the beau- 

 tiful results which Melloni obtained with his thermo-electric 

 pile in his researches on radiant heat. 



M. Pouillet has used the same principle for the measure- 

 ment of high temperatures t; and he has described, under the 

 name of magnetic pyrometer, an apparatus which is compared 

 with his air pyrometer, and by means of which he states that 

 he is able to measure the highest temperatures of our furnaces. 



* Extracted from his Recherches sur la Chaleur. This is the memoir of 

 which we promised to give a full translation in our former notice of M. 

 Regnault's experiments, p, 56 of the present volume. — Ed. 



t Elemens dc Physique, 4th edit. vol. ii. p. 684. Comptes Rendus, vol. iii. 

 p. 786. 



Phil. Mag, S. 3. Vol. 36. No. 24-5. June 1850. 2 E 



