Stress on the Electrical Conductivity of Met ah 

 Results. 



639 



Manganin wire. — The manganiu wire used was *1 mm. 

 diameter, double silk-covered, and was arranged as described 

 above. 



The following readings were obtained : — 



Pressure in 

 Atmospheres. 



Change of 

 Resistance, 

 dR jq 4 



Change per 

 Atmosphere, 



10-5 



•23 



22-5 



31 



91 



•66 

 2-00 

 4-12 



21-3 

 21-7 

 21-3 

 23-0 

 22 5 

 221 

 22*1 



192 .., 



292 



6-39 



8-59 

 10-82 



392 



492 



592 



13-13 



The resistance is increased by pressure, and the increase is 

 within the limits of experimental error directly proportional 

 to the pressure, the mean value being : 



^ R = 22-2 . 10" 



IX 



per atmosphere. 



This is the actual change o£ resistance observed. To obtain 

 the change of specific resistance it is necessary to correct for 

 the change of dimensions of the wire due to its compressibility. 

 As the compressibility of manganin is not known, it is im- 

 possible to calculate the value of this correction. A rough 

 approximation may, however, be obtained by assuming the 

 compressibility to be the same as that of copper, viz. '83 . 10~~ 6 

 per atm., and with this value the change of specific re- 

 sistance is 



18'2 . 10~ 7 per atmosphere. 



Lead Wire. — The arrangements were precisely the same 

 as those employed for manganin wire. The dimensions of 

 the lead wire were : diameter *37 mm., length 1*5 metres. 

 Resistance 3" 28 ohms. 



The readings obtained were: — 



