316 M. Becquerel on a method of measuring 



cal effects less strong in proportion as the temperature in each 

 of them is raised. 



We might perhaps be led to believe that the rise of tempe- 

 rature, diminishing the conducting power of the metallic wires, 

 the apparatus does not then show all the increase of the elec- 

 tro-dynamic intensity which takes place from the rise of tem- 

 perature. But this opinion is destroyed by experiment ; for 

 if we operate at moderate temperatures, which give distinct ef- 

 fects, and if we bring to a red heat a part of the circuit remote 

 from one of its joints, the diminution of the conducting power 

 is not sufficiently sensible to alter the results obtained before 

 the experiment was made. This fact seems to contradict the 

 observation of Sir H. Davy, who has found that a conducting 

 wire allows less and less electricity to pass in proportion as we 

 raise to a red heat the temperature of a small portion of its cir- 

 cuit. But it is easy to reconcile these apparently contradictory 

 results, for Sir H. Davy has shown that when we make a small 

 quantity of electricity pass through the conducting wire, the 

 least change in the conductibility of the place where the elec- 

 tric fluid has not the power of extending itself, ought to dimi- 

 nish sensibly the quantity of electricity which it transmits ; 

 whereas, when we come to pass only a very small quantity of 

 electricity, we may conceive that the fluid, not experiencing any 

 difficulty in extending itself, a diminution in the conductibility 

 ought to allow to pass nearly the same quantity, which is con- 

 firmed by experiment. 



Art. XXI. — On a method of measuring High Tempera- 

 tures. By M. Becq.uerel. * 



We have seen in the preceding pages, that a metallic cir- 

 cuit, formed of a palladium wire and a platina wire, possesses 

 the property, where one of the joints is raised successively 

 from 0° to 350° of temperature, of giving equal increments 

 of electro-dynamic intensity for equal quantities of tempera- 

 ture. 



* This article forms the third part of the preceding paper. We have 

 given it separately, in order to excite that attention which it so well merits. 

 Ed. 



