118 Mr. T. C. Mendenhall on Edison's Tasimeter. 



■ T ™ e ' Resistance. . Ti . me ' Resistance. 



in minutes. — »•» <- m mmu tes. 



100 15 H2-9 



1 96-6 20 92-5 



2 95-4 25 92-3 



3 94-9 30 92-1 



4 94-5 35 92-0 



5 94-2 40 91-8 



6 93-9 50 91-5 



7 93-7 60 91-2 



8 93-6 70 90-9 



9 93-4 80 90-8 



10 93-3 90 90-7 



12 93-1 



It will be seen that the resistance falls a little more than 

 3 per cent, in one minute, about 5 per cent, in three minutes, 

 and about 10 per cent, in one and a half hours: and it seems 

 tolerably certain that even then a minimum is not reached. 

 In two or three instances the time of continuous pressure was 

 prolonged to twenty-four hours, the resistance at the end being 

 slightly lower than at any previous reading. Finally, the 

 apparatus was left with the weight applied for one week. 

 No measurements were made during that time; but at the end 

 the resistance was found to be decidedly lower than it was at 

 the end of two hours after the application of the pressure ; 

 and it is especially to be noticed that, on the removal of the 

 pressure, the normal resistance of a week before was instantly 

 recovered. In this case the pressure applied was 100 grams. 

 The resistance before the application of the pressure was 11-08 

 ohms. Upon applying the pressure, it immediately fell to 

 2 "34 ohms. In two hours this had been reduced to 2'10 ohms; 

 and at the end of a week it was 1*93 ohm. Thus in two hours 

 it was reduced by about 10 per cent.; and after one week it 

 was again about 10 per cent, lower. 



It appears, therefore, that the element of time plays an 

 important part in the phenomena exhibited by the carbon disk; 

 and it seems highly probable that this has been one of the 

 principal causes, if not the chief cause, contributing to the 

 inconstancy and unreliability of the indications of the tasi- 

 meter. The experiments made thus far indicate a fair degree 

 of constancy in its results when this factor is considered. The 

 writer hopes to be able to make further examination concern- 

 ing the extent to which all the conditions necessary to its use 

 maybe controlled. 



The resistance of carbon under pressure has been made the 



