476 



PEOCEEDINGS OF THE AMERICAN ACADEMY. 



first, the difference in the capacities of the air condenser and the test 

 condenser; and, second, to the residual charge which had time to 

 form during the charging interval. The test condensers "Mica A ," 

 "Mica B , " and "Par. A" were adjusted to give very small throws 

 when the charging interval was thus cut down as far as possible. But 

 it is important to notice that this small throw does not necessarily 

 measure the difference in the capacities of the condensers. For although 

 the charging interval is indeed small, yet if it were reduced still further, 



0.05 



0.10 0.16 



TIME IK SECONDS. 



Figure 2. (Tables I and II.) 



the air condenser might gain in apparent capacity on the test condenser, 

 and the small throw, after perhaps first passing through the zero 

 value, if it was at first in favor of the test condenser, might finally 

 increase and keep on increasing. In other words, it is only when the 

 small throw is in favor of the air condenser, that is, in the direction in 

 which a throw coming from the air condenser by itself would read, that 

 we can assert that the capacity of the air condenser is greater than that 

 of the test condenser, for if the throw is in favor of the test condenser, 

 we do not know whether the residual charge formed is less, equal to, 

 or greater than, this charge causing the small throw. In fact, we see 



