364 O. N. Rood on the Electric Spark. 
vantage of this mode of experimenting is, 
When the poles of the induction coil are united by a metallic 
or liquid conductor, on completing the voltaic circuit, a current 
is induced in the induction coil which circulates in the opposite 
current circulating in the opposite direction from the first. 
In this case, the poles of the coil are alternately positive and 
_arapidly revolving mirror, and find it made up of a very con 
siderable number of discharges, but according to what has been 
above stated, they are not to be regarded as oscillatory, but 
_ (it is hoped,) can hereafter be applied to the elucidation of more 
ie 
Viz: that which is formed on the sensitive plate used as negative 
"Length of the discharge 1’, of an inch, 
