69-4 Mr. S. C. Laws on the Change of Resistance of Metals 



The proportionality between — and H 2 is again apparent 

 as in the case of cadmium. ^ g r 



The following table shows also the value of rp— a ^ 

 different temperatures. 



H. 



i-XWP. 



H 2 r 



t^m% 



^=18-5. 



t- -186. 



3680 



3800 



4060 



8200 



9110 



10200 



10900 



11700 



12100 



12700 



"•54 

 •56 

 •54 

 •53 

 •54 

 •57 



•93 

 •92 



•85 

 '83 

 •82 

 •85 

 •89 



150 



17 

 220 



•54 ^87 



18'0=niean. 



Experiments with Carbon. 



A considerable portion of the time devoted to the experi- 

 ments described in this paper was occupied in the examina- 

 tion of the change of resistance of carbon in the magnetic 

 field. The work was unsatisfactory in the first place because 

 of the very wide range of value observed for different 

 specimens of carbon, and secondly because in the case of 

 graphite, which alone gave anything like consistent results 

 at atmospheric temperature, the resistance was altogether 

 too unsteady for the purposes of this experiment as soon as 

 the temperature was raised. 



This difficulty seems to be inherent in the nature of the 

 material. In liquid air, however, the resistances were quite 

 steady. 



The earlier experiments were made with the carbon fila- 

 ments from incandescent lamps, but it was found that whilst 

 sonie filaments showed practically no change of resistance 

 in the magnetic field, others again showed as large a change 

 as 0'5 per cent, in a field of 10,000 C.G.s. units. This change 

 of resistance was found to take place in the outside layer of 

 deposited carbon 3 for when thjs was removed by burning or 



