86 EMPLOYMENT OF ELECTEICITY 



uniform direction of the current, as marked on 

 the indices Pos. and Neg., is always insured ; a 

 desideratum of considerable importance, since 

 the effects or rather the sensations produced by 

 the negative terminal are much more pungent 

 than those of the positive. 



6th. The whole of the apparatus, including coil, 

 battery, stoppered bottle to contain dilute acid, 

 shock-handle, insulated wires, and spring foot- 

 board, are contained in the little box six inches 

 long, six inches high, five inches wide, and the 

 battery and coil- work, without being taken out of 

 the box. 



In the spring footboard which I employ, I sus- 

 pend the current by the depression of the spring, 

 and cause it to pass by removing the foot, the 

 elasticity of the spring making its own contact. 

 The spring not being in connection with the 

 machine when depressed, the foot which is placed 

 upon it does not become a conductor to the shock, 

 as is the case frequently, if this precaution be not 

 observed. 



Having naw described the machine, which I 

 trust will be found as efficient and free from 

 objections as may be desired, I proceed to notice 

 its employment and connection with dental in- 

 struments. 



The main object to be obtained is the trans- 

 mission of a current of electricity, or a rapid 

 succession of minute vibratory shocks, through 



