242 WRITINGS OF JOSEPH HENRY. [1845 



He next passed to the connection between statical and 

 dynamical induction. Statical induction has heretofore been 

 observed only at short distances. His first experiment 

 proved that it could be observed at the distance of nineteen 

 feet, the floor of a chamber intervening, showing that stati- 

 cal induction takes place at great distances, though not at so 

 great distances as the dynamical. He then explained his 

 views of the nature of dynamical induction. When a spark 

 is thrown upon a wire it passes in a wave, whose length 

 might be determined if we knew the velocity of electricity. 

 Now, if we have another parallel wire, a negative wave will 

 be formed in this, and the two waves will travel simulta- 

 neously in the same direction. But this is equivalent to a 

 positive induced wave in the opposite direction. In this 

 way the phenomena accompanying the discharge of a jar are 

 easily explained. Again, if we conceive that in a galvanic 

 battery the discharge consists of a series of such waves, we 

 may very simply explain the phenomena of galvanic in- 

 duction. 



