556 Dr. 0. J. Lodge on the Specific Electrical 



To get the value of the bridge-wire-readings in absolute 

 measure, a half-ohm coil of German-silver wire at the tempe- 

 rature of the room (t. e. of the bridge-wire) was inserted in 

 the place of the rods, and readings taken of the steps corre- 

 sponding to it. The scale of magnification was of course again 

 observed. Instead of being about 3*6, it was now about ^. 



The result of the whole series of measurements may be 

 summed up in the following Table: — 



Specific Resistances of the six Copper- Tin Alloys 

 in square centimetres per second. 



A 12960 



B 10960 



C 47660 



D 11830 



E 17090 



F 15270 



I consider these accurate to the second figure, the third 

 figure is probably affected by experimental errors. 



If we choose to express the results in terms of conductivity, 

 we have the following: — 



Conductivity of a Centimetre Cube of the six Alloys 

 in B.A. units. 



A 77100 



B 91200 



C 21000 



D 84500 



E 58500 



F 65500 



The specific resistance of the alloy C is thus four times that 

 of B or D. 



The composition of the alloys by weight, Mr. Roberts in- 

 forms me, is as follows : — 



A . . . 19*2 per cent, of copper 80*8 tin. 



„ „ 38*2 „ 



?> » 31*7 „ 



100-0 „ 



12-6 „ 



0.7 



Some of these alloys were examined by Matthiessen, viz. 

 A, D, E, and F ; and the conductivity of a wire 1 metre long 

 and 1 millimetre thick is stated by him to be, in terms of the 

 B.A. unit, 



of the metal A 6*0 



,, D (pure tin) . . 5*9 



B 4-2 



F 5-9 



B . . 



. 61-8 



C . . 



. 68*3 



D . . 



. o-o 



E . . 



. 87-4 



F . . 



. 90*3 



