490 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



centage of total "free charge," without giving all the individual ob- 

 servations. The meaning of the positive and negative ballistic throws 

 and the method of making the reductions is fully described on page 

 500, in connection with the results of March 10 and 11. 



It should be noted here that various resistance coils, from 5 to 85 

 ohms and higher, were used in the condenser circuits, connected 

 directly to one of their terminals as indicated by small circles (fr) in 

 the diagram. Usually, however, the air condenser had a 10 ohm coil, 

 and the test condenser a 5 ohm coil, connected to it. The exact value 

 of the resistance is not important ; the object of the resistance is merely 

 to prevent too great an initial rush of charge. 



All the pieces of apparatus, the storage battery, the falling weight 

 machine, the condensers, the commutating keys, and the galvanometer, 

 were carefully insulated by means of large porcelain knobs or blocks 

 of paraffin. These were often cleaned and scraped and, so far as could 

 be ascertained, none of the troubles experienced were due to leakage of 

 any kind. It will be noticed later that the air condenser and most of 

 the test condensers have a small internal conductivity, but as the opera- 

 tion of neutralizing the charges takes place immediately after the 

 charging, this conductivity could not result in a measurable loss of 

 charge from either condenser. 



On February 26 a condenser made up of 12 separate commercial 

 paraffined paper condensers, giving a total capacity of about 50 micro- 

 farads, was connected across the terminals of the storage battery. 

 This was done to avoid a possible source of trouble in that the battery 

 might not be able to furnish complete charges for the test condenser in 

 the very short charging intervals. It was found to be useful, but the 



TABLE XI. (Figure 7.) 

 " Par. A " vs. Air. February 11. 



