272 Prof. E. Wartmann's third Memoir on Induction. 



double helix is pierced in tlie centre by an aperture of C^'O'l 

 in diameter, in which may be fixed a bundle of soft iron wires, 

 or a liollow cylinder of iron plate furnished externally witli 

 similar vvires. 



111. It is especially in valuing the lieating eflects of which 

 the induced currents are capable, that we seek to resolve the 

 proposed problem. After having placed in the circuit of the 

 long wire Breguet's thermometer (4. c), and having deter- 

 mined the number of alternate induced currents, which in the 

 unit of time give the maximum of heating, an hydro-electric 

 current was passed into the wire and into the thermometer. 

 The inductor current was that of five large pairs of Daniell 



1 12. Ihe following results were obtained : — 



a. The calorific eflect of the currents of induction is more 

 considerable w hen the bundle of wires is placed in the helix 

 than wlien the hollow cylinder is employed : the latter being 

 removed, the temperature again decreases, 



b. The result does not vary whether the induced wire is or 

 is not traversed by a constant current. 



c. The elevation of temperature of the thermometer pro- 

 duced by a continuous and constant current, which traverses 

 a wire formed into a helix, is independent of the presence or 

 absence of bundles of soft iron vvires, solid or hollow, placed 

 within it. 



113. I have had constructed a large pair, of bismuth and 

 soft iron, 0™"2 long, and the square section of which is 0'"'022 

 at the side. The free extremities of these metals were bound 

 to a thermo-electric rheometer (46) by a wire long enough 

 for the instrument to be protected from all magnetic induc- 

 tion. 



114. No appreciable current tvas j^f'oduced on placing the 

 pair in the large helix (3), and developing in it an intense 

 electro-magnetic state with a Bunsen's battery of twenty 

 elements. 



115. The soft iron of the couple was enveloped in an iso- 

 lated copper wire. Then, after having heated its solder to a 

 constant temperature and determined the force of the thermo- 

 electric current produced, a hj'dro-electric current was passed 

 into the wire. The deviation of the rheometer did not vary, 

 notwithstanding the electro-magnetic state induced in ihe 

 iron. 



