696 Mr. S. C. Laws on the Change of Resistance of Metals 



July 8th, 1909. 

 r *=-186°. Y = l02. X=505. r = 0'660. 



c. 



H. 



Deflexion on 

 reversal. 



£rxl0 4 . 



St 



-xio 4 . 



r 



H 2 xl0 _7 . 



— -xlO" 



1-8 



2580 



112 



106 



163 



•665 



242 



2-5 



2900 



138 



131 



19-8 



•84 



236 



34 



3220 



160 



15-2 



230 



1-04 



225 



4-4 



3360 



182 



173 



262 



113 



223 



5-6 



3660 



203 



19-3 



29-2 



1-34 



217 



75 



3940 



230 



21-8 



33-2 



1-56 



215 



100 



4140 



256 



243 



36-8 



1-71 



215 



225 = mean. 



These results indicate that for graphite the change of 

 resistance varies approximately inversely as the absolute 

 temperature : the change of resistance in a given field 

 increases threefold between the temperatures 18° O. and 

 — 186° C., whereas in the case of the metals examined the 

 change of resistance at the temperature of liquid air is about 

 20 times that at atmospheric temperature. 



In endeavouring to maintain the resistance of graphite 

 constant at higher temperatures, I made some experiments 

 with fairly satisfactory results with the substance in the 

 form of powder. 



The pow r dered graphite was enclosed in the form of a 



cylinder about 1 mm. diameter and 6 mm. in length, along 



the axis of a short wooden cylinder fitting into a hole drilled 



in a small piece of brass, and was maintained in a state of 



compression by means of a vertical brass plunger. This 



plunger was forced down upon the graphite by the pressure 



exerted by the short firm of a lever, to the long arm of 



which an upward force was applied by means of a suitable 



weight suspended over a pulley. These experiments, which 



were made at temperatures of 17° and 98° with fields ranging 



from 4300 to 6930 c.G.s. units, indicated that between these 



1 8r 

 limits of temperature the values of ^ — diminished in the 



ratio of 1'2 to 1. As the absolute temperatures are in the 

 ratio of 1 to 1*28 these experiments serve to confirm the 

 results previously given for graphite rod. 



As already mentioned, any explanation of electrical con- 

 duction in metals in terms of the original corpuscular theory 

 as developed by Sir J. J. Thomson, Lorentz, and others, and 

 according to which conduction is due to a system of freely 



