6 Profs. J. Dewar and J. A. Fleming. On the Dielectric 



Fig. 1. 



electrically controlled tuning fork. The tuning fork used made 124 

 complete vibrations a second, and was made, by means of a mercury 

 cap and steel stylus dipping into it, to close an electrical circuit 124 

 times every second, and thus drive synchronously an electro-mag- 

 netic contact maker, which placed one terminal of the condenser 

 alternately in connection with a battery of fifty iithanode secondary 

 cells, and with a sensitive galvanometer. The other terminals of the 

 battery, galvanometer and condenser, were connected together. In 

 this way the galvanometer was traversed by a rapid series of electric 

 charges, which have all the effect of a continuous current. The 

 galvanometer deflection remains perfectly steady as long as the battery 

 voltage is unaltered. Other things remaining the same, the galvano- 

 meter deflection measures the capacity of the condenser. In employ- 

 ing this method, the galvanometer may be arranged so as to be 

 affected by the series of discharges of the condenser, or it may be 

 placed so as to be traversed by the series of charges of the condenser. 

 If the condenser has any sensible leakage or dielectric conductivity 



