Iron under Alternating Magnetic Force. 



219 



by means of a liquid (CuS0 4 dil.) reverser consisting of two oppositely 

 fixed copper plates, each embracing a quadrant of a circle, and two 

 similarly shaped copper plates fixed to a vertical spindle and capable 



Fig. 1. 



Fig. 2. 



of rotating concentrically within the fixed plates. The operator at 

 this liquid reverser counted seconds aloud whilst listening to the ticks 

 of a seconds pendulum. In this way the epoch for all the observa-. 



VOL. LXVIII. R 



