326 Dr. M. Maclean. On the Effects of Strain 



Copper 99*4 per cent. 



Arsenic 0'44 



. Lead 0-08 



Bismuth . . trace 



99-92 



(3) Copper wires, used for alloying with gold and silver, from Messrs. 



Johnson and Matthey. This also was analysed and it con- 

 tained 99-85 per cent, of copper. 



(4) Copper wire from Glover. Chemical analysis showed that it 



contained 98' 35 per cent, of copper. 



(5) Copper wire of Glover's manufacture and supposed to be soft 



and to have a very high conductivity. It contained 99-08 per 

 cent, of copper and 0*22 per cent, of lead. 



(6) Copper wire used in laboratory experiments. It contained 



98-51 per cent, of copper. 



(7) Lead wire, commercial. It contained 98*9 per cent, of lead. 



(8) Lead wire, pure.* It contained 98'97 per cent, of lead. 



(9) Platinoid wire obtained from Messrs. Glover. 



(10) German silver wire 



(11) Eeostenet 



(12) Manganin 



9. The size of the wire used, except for (5) (7) (8) above, was about 

 No. 18 standard gauge. A piece of the wire was taken and drawn 

 through a draw plate till it was reduced to about No. 24 standard gauge. 

 This process of wire drawing subjects the wire to longitudinal extension 

 and to lateral compression. Lord Kelvin in his experiments (' Mathe- 

 matical and Physical Papers/ vol. 2 and section 3 above) showed that 

 thermo-electric differences were in the same direction for longitudinal 

 extension and transverse compression. For drawn and undrawn wires 

 the direction of the current through the hot junction is from undrawn 

 to drawn for copper, reostene, and lead, and from drawn to undrawn for 

 platinoid, German silver, and manganin. The magnitude of the current 

 per degree difference of temperature is given in the following table. 



* These specimens of commercial and pure lead wires were obtained from 

 Messrs. Baird and Tatlock of G-lasgow. Other specimens have been ordered else- 

 where for a fresh determination. 



t Reostene belongs to the uickel steel group, with certain other metals as an 

 alloy. Messrs. Grlover and Co. could not give me particulars regarding it, or 

 i*egarding manganin, which is composed of copper, tin, and manganese. 



