IN DENTAL OPERATIONS. 85 



not only enables me to use a shorter secondary 

 coil, and thereby increase the compactness of the 

 instrument, but it also affords an opportunity of 

 using very strong interrupting springs which 

 insure better contacts and more uniform action, 

 and which vibrate with immense rapidity, causing 

 the shocks to follow each other with correspond- 

 ing velocity. 



3rd. The secondary coil is so arranged as to 

 take up the whole of the electricity induced by 

 the core, and is subdivided, by means of an index 

 and graduated buttons, into four equal degrees of 

 power, each of which, by means of a second index, 

 is again subdivided into quarters, thus giving a 

 range of 16 equal and delicate increments of force, 

 perfectly under the control of the operator. The 

 advantage of this arrangement is, that the unit 

 of force being extremely small, the rate of increase 

 can be always accurately measured, and no more 

 electricity is by any' accident capable of passing 

 than the precise quantity excited in the portion 

 of secondary coil embraced between the terminals. 



4th. All these graduations being of precisely 

 the same value, different operators have accurate 

 means of comparing their results; since, if the 

 apparatus be kept' in proper working order, the 

 corresponding degrees of each machine will be 

 found to be equal. 



5th. The battery being connected with the 

 machine in one determinate manner only, the 



