Nickel Stress Telephone. 27 



round which a coil of insulated wire has been wound, is fixed 

 in a vertical position by a clamp at its lower end, and that 

 its upper end is fastened to the centre of a light horizontal 

 plate, which serves as a diaphragm. On speaking against 

 the top of the diaphragm variations of longitudinal pressure 

 and consequently of magnetization will be produced in the 

 nickel wire, and hence a varying current will be induced 

 in the coil. If the coil be connected with any kind of 

 receiving telephone the speech will be reproduced. 



We have made a large number of experiments with the 

 object of determining the form of instrument which would 

 give the best results ; but owing to the difficulties of 

 comparing the speaking powers of different instruments we 

 found it impossible to say with certaint}'- which form was the 

 best. The details of one of the forms with which good 

 results were obtained are as follows : — The nickel wire was 

 10 cm. long and 1 mm. in diameter. The clamp was formed 

 of a massive piece of gunmetal (an ordinary workshop vice 

 will do quite as well) and the diaphragm was a circular disk 

 of pine wood 3*5 mm. thick and 12*5 cm. in diameter. A 

 hole was made through it in the centre into which the nickel 

 wire was stuck with sealing-wax. This diaphragm was 

 entirely supported by the nickel wire. The coilconsisted of 

 3*9 grms. of No. 40 B.W.G. silk-covered wire wound directly 

 on the nickel wire. The length of the coil was about 7*5 cm. 

 An ordinary watch telephone, the resistance of the coils of 

 which was about 136 ohms, was used as a receiver. The 

 resistance of the line was quite small, as all the experiments 

 were made from one room to another in the same building. 

 The nickel wire was sometimes magnetized by stroking it 

 with a magnet, sometimes by sending a current from a few 

 Leclanche cells through the coil. Whether the wire was 

 annealed or not appeared to be immaterial. Wires of various 

 dimensions were tried, but the results obtained were not very 

 different. With a diaphragm made of pine wood, the results 

 were decidedly better than with a metallic diaphragm 

 articulation then being very clear. It was found to be better 

 to use a clamp of considerable mass. 



When the nickel wire was replaced by an iron wire the 

 results obtained were very feeble. 



The same instrument was also used as a receiver. With an 

 iron wire it worked very badly, with a nickel wire it worked 

 rather better but not at all well. Since beginning our expe- 

 riments we have found that M. Ader* has used as a receiver 



* Comp. Bend. 1879, t. lxxxviii. p. 575. 



