12 



Mr. S. Bidwell. 



[Feb. 1 T 



Table IX. 



R 1 = Resistance with current in first column of table. 

 R 2 = Resistance with very weak current. 





Pressure. 



Current. 

 Ampere. 



•05 grm. 



•5 grm. 



2 5 grms. 



5 grms. 







E 2 . 





E 2 . 



% 



E 2 . 





E 2 . 



•01 



•05 



•1 



•2 



•3 



•4 



'5 



•6 



•7 



38 

 21 

 Inf. 



62 

 38 



10 2 

 9-7 

 8-1 

 6-3 

 Inf. 



10 3 

 10-1 

 9-3 

 8-4 



4-8 

 4-6 

 4 -4 

 4-0 

 3-7 

 3 6 

 Inf. 



4-8 

 4-7 

 4-7 

 4-5 

 4 3 

 4-2 



2-60 

 2-54 

 2-37 

 2 23 

 2-11 

 2-01 

 1-95 

 1-90 

 Inf. 



2-6 

 2-6 

 25 

 2-4 

 2 3 

 2-3 

 2 2 

 2 -2 



10. Experiments with Metallic Contacts. 



For the sake of comparison a few experiments were made with 

 metals. Metallic loose contacts were found to be even more uncertain 

 in their action than those of carbon, and to obtain a really fair 

 average of results a very great number of measurements would be 

 required. Under precisely the same conditions as nearly as they 

 could be reproduced, the results obtained were frequently very 

 different. Nevertheless it has been possible to bring out with suffi- 

 cient distinctness some remarkable peculiarities in the behaviour of 

 metallic contacts. 



The metal principally used was bismuth, which was selected on 

 account of its high specific resistance ; but a few experiments were 

 also made with copper and platinum. The cylinders of bismuth and 

 copper were nearly the same diameter as those of the carbon pre- 

 viously used — 6 millims. The platinum was prepared by soldering 

 wires of that metal upon cylinders of brass. The balance already 

 described and shown at fig. 1 was used in the same manner as before. 



11. Permanent Fall of Resistance caused by Current. 



The first unexpected phenomenon which attracted notice in working 

 with bismuth was the very great permanent fall in the resistance 

 which was produced by an ordinary current with light pressures. 

 Using a single Leclanche cell, the lightest contact — the pressure being 

 certainly less than *01 grm. — failed to give a higher resistance than 



