14 



Mr. S. Bidwell. 



[Feb. 1 ? 



the scale-pan, let a weak current be caused to pass through the points 

 of contact; the resistance will be found to be high. Let a strong 

 current be passed, and the resistance will be greatly diminished. 

 Once more let the current be reduced to its original strength ; the 

 resistance will not rise to its original value ; it will not, in fact, rise at 

 all; it will be still further diminished. The following table gives 

 examples of this experiment with pressures of "5, 1, and 5 grms. 



Table XL 



Current. 

 Ampere. 



Eesistance of bismuth contacts -with 

 pressure of 



•5 grm. 



1 grm. 



5 grms. 



•01 



8 



2 12 



1 '50 



"5 



1-27 



1-27 



122 



•01 



1-22 



121 



1-22 



•5 



1-27 



1-26 



1 22 



•01 



1-22 



1-21 



1 22 



In the last case there is no change after the first fall of resistance. 

 Table XII further illustrates the effect with greater variations of 

 current and of weight, but in the experiments to which it relates the 

 strongest current was used first. As before, the bismuth cylinders 

 were separated only when the weights were changed. 



Table XII. — Experiments with Clean Bismuth. 







Eesistance of contacts with pressure 



of 



Current. 















Ampere. 

















•25 



grm. 



•35 grm. 



*5 grm. 



1 grm. 



2 grms. 



'5 



1 



•52 



1 39 



1 55 



133 



1 -35 



•3 



1 



'40 



1-35 



1 -49 



1 30 



1 -33 



•1 



1 



•37 



1 -33 



1-45 



1-28 



132 



•05 



1 



•35 



1 33 



1-44 



1-28 



1-32 



•01 



1 



•18 



132 



1-41 



1 -28 



132 



•05 



1 



•55 



1 33 



1-46 



1 -29 



1-32 



1 



1 



•72 



1 34 



1 -47 



1-29 



1 33 



•3 



1 



•79 



1 -39 



1 '55 



1 -31 



1 34 



•5 



1 



•49 



1-48 



1-61 



1-33 



135 



In order that this experiment may be successful, it is necessary that 

 the surfaces in contact should be absolutely clean. Unless they are 

 scraped immediately before the measurements are made, the opposite- 



