2l6 



SCIENTIFIC RECREATIONS. 



The glass will be found pierced by the electric spark when the Leyden jar 

 is brought into requisition (fig. 217). 



It was at one time contended that the sudden expansion of the air by 

 the electric spark caused heat to be generated, and a thermometer was 

 invented by Kinnersley to show this. The illustration (fig. 2 I 8) will explain 



Fig. 2 1 7. Experiment with glass. 



Fig. 2 1 8. Kinnersley 's thermometer. 



it. When the electric spark passed between the balls in the large tube the 

 water rose in the smaller. But the immediate return of the water to its level 

 showed that the disturbance was only mechanical, and not owing to heat. 



We may now pass from the " frictional " to the other kind viz., 

 " dynamical " electricity, and we shall begin with the consideration of 

 GALVANI'S experiments and the VOLTAIC PILE. 



Electric condenser. 



