Stress on the Electrical Conduct! city of Metals, 641 



Braun) was used in the experiments. One o£ the mica plates 

 which protect the spiral was removed, the other being left to 

 support the wire. The spiral was placed in the rubber tube 

 as used in the previous experiments. The resistance of the 

 spiral was 26 ohms and the diameter of. the wire "25 mm. 

 The readings obtained were : — 



Pressure in 

 Atmospheres. 



Change of 

 Eesistance. 



Change per 

 Atmosphere, 



dn 10* 



31 



63 



18-6 

 57-7 

 95-7 



200 

 201 

 197 

 194 



92 



292 



492 





The resistance of bismuth is increased by pressure, the 

 ™ mean value of the increase being : 



=f #^ dH inn in v i i 



-^- = iyb . 10""' per atmosphere. 



Bismuth is the only one of the pure metals 

 so far investigated whose resistance is increased 

 by pressure. 



ilr 



Influence of Tension on the Resistance of 

 Bismuth. 



The Lenard's spiral used in the previous 

 experiment was unwound and two pieces of 

 wire about 10 cms. long were obtained. These 

 were soldered to two copper terminals of the 

 form shown in fig. 3. The two wires were 

 then placed in a wide glass tube filled with oil 

 and suspended vertically as shown. The upper 

 terminal of one wire was hung from the arm 

 of a balance, and the wire was stretched by 

 hanging weights from the other arm. The 

 two wires were arranged in adjacent arms of 

 a Wheatstone's bridge, the two upper terminals 

 dipping into a mercury-cup connected to the 

 galvanometer. The whole arrangement was 

 covered with a thick cloth to protect it from 

 air-currents, and when this was done a fairly 

 steady zero was obtained. 

 Phil. Mag. S. 6. Vol. 13. No. 77. May 1907. 2 X 



