in a Magnetic Field at Different Temperatures. 095 



scraping all filaments agreed in showing no change of 

 resi.stance. 



The filament from an ordinary Ediswan 16 c.p. 110 V 

 filament gives a value of the order of 0*5 per cent, for the 

 change of resistance in a field of 10,000 C.G.s. units. The 

 high voltage filaments show very little change of resistance 

 in the magnetic field. 



Also unflashed filaments specially supplied by the Robert- 

 son Company and ordinary filaments from their lamps 

 similarly showed no change, but some that they flashed for 

 me showed a change which was larger the greater the amount 

 of flashing. 



Though this layer to which the change of resistance was 

 due could be easily removed, it was not obtainable again by 

 the process of flashing in coal-gas or various liquid hydro- 

 carbons which I tried. 



Owing to this lack of uniformity in the incandescent lamp 

 filaments, I made experiments with graphite, which was found 

 to show a considerable change of resistance in the magnetic 

 field. 



Experiments have been made on the impure graphite from 

 numerous specimens of lead pencils as well as with some 

 specimens of pure graphite supplied by the Morgan Crucible 

 Company. 



These all agree in showing a change of the order of 1 per 

 cent, in a field of 10,000 units (and also in having an un- 

 certain resistance at temperatures higher than atmospheric). 



Below are tabulated the readings taken with a specimen 

 of pure graphite, at 15°*5 C and in liquid air. 



.> \>. 



July 8th, L909. 

 Y = 88. X=516. r=0521. 



c. 



H. 



Deflexion on 



tVxlO 1 . 



^Xl0». 



IFxlO"" 7 . 



H- v 







reversal. 





/■ 





1-8 



2580 



825 



283 



6-43 



•665 



81-7 



2-5 



2900 



in I 



348 



6-68 



•84 



79-4 



3-4 



3220 



47a 



413 



7-92 



101 



77-:> 



44 



3360 



541 



470 



9-02 



113 



7<i 7 



5-6 



3660 



621 



;»•:;•♦ 



in 1 



1 -:;4 



7K-8 



7-5 



3940 



74 



640 



L2-3 



1 ;,h 



79*5 



KM) 



4140 



783 



6-7'J 



l:; 1 



1 71 



761 



78*2= mean. 



