272 Mr. G. Kamensky on the Electric Conductivity 



indicated by Prof. W. Chandler Roberts*, who has shown that 

 the necessary information as to the electrical position of alloys 

 may be readily ascertained by the induction-balance; and the 

 accuracy of his view was subsequently confirmed by Dr. 

 Oliver Lodgef, who used the Wheatstone bridge. The method 

 adopted in the case of the induction-balance consists in placing 

 the disk to be examined on one side of the balance, and in 

 superposing a graduated wedge-shaped scale of zinc over the 

 opposing coil. This method has already been described by 

 Prof. Roberts, who has lent me the graduated zinc scale by 

 which his numbers representing the " induction-balance effect '* 

 of various alloys were made. 



It is true that the numbers named by the use of this scale 

 are arbitrary ; but they can be controlled by employing disks 

 of pure metal of known resistance, provided that they have 

 the same dimensions and volume as the disks of the alloys 

 under examination. 



The alloys were cast direct into the required 

 disks, which was managed by using an ingot-mould 

 in which a steel plate cut out, as here shown, was 

 inserted. The disks so cast were ground down 

 on a stone to a thickness of 3 centim. 



In mapping out the curve of Electric Con- 

 ductivity, I decided, after consultation with Prof. 

 C. Roberts, not to give the number obtained for 

 the disk of copper, as in his opinion that cannot 

 be determined for a disk of the same size as the 

 rest of the series by the particular zinc scale used. 



I here give the readings obtained with the balance : — 



No. 1. ... 



„ 2. ... 



» 3 



. „ 4. ... 



„ 5. ... 



» 6 



» 7 



„ 8 105*5 



9. 

 10a. 



58 

 69 

 74-5 



77 

 87 

 89 



120 

 121 



No. 11 85 



12. 



13. 



13a. 



14. 



15. 



16. 



17. 



18. 



57 

 52 

 48 

 53 

 60 

 63 

 65 

 77 



It will be seen that the curve, viewed as a whole, is of the 

 L shape, which Matthiesen found to be characteristic of the 

 chiss of alloys of which the copper-tin series is the type. 



* Phil. Mag. July 1879. 



t Phil. Mag. February 1880. 



\ Loc. cit. 



