lyU ELECTRICAL CONSIDERATIONS. 



The rate of their occurrence depends upon the length of the spring. 



Explanation : The current from the battery flows up the pillar C, 

 through the spring up through the top contact screw to the P coil, and 

 thence round the electromagnet F and back by the base of D to the 

 battery. 



When the current flows round the circuit, F is magnetised and draws 

 down the spring I, thus breaking the top contact. 



Upon this the current stops flowing, the magnet ceases to act, the 

 spring is released and again makes contact with E, and so the circuit 

 is re-established and the cycle begins anew. 



As the break shock is always the stronger of the two, it follows that 

 if these shocks are passed through a tissue for some time that polarisa- 

 tion effects will be set up. Ordinarily they are employed for a short 

 time only, and this effect can be disregarded. In cases in which this 

 may be of importance the next arrangement must be made use of. 



SINGLE 



INTERRUPTER HELMHOLT2 



FIG. 28. Connections of the primary circuit (after Waller). 



Helmholtz wire for the equalisation of the make and break shocks 

 (Fig. 28). Leave the connections as for interrupter shocks and add a 

 wire between G and A. Raise the top contact screw E clear of the 

 spring, and turn up the screw on pillar D until it touches the under 

 side of the spring when the latter is held depressed against the electro- 

 magnet. On closing the circuit the spring oscillates. 



Explanation. The P circuit is now closed at all stages of the oscillations of 

 the spring. 



When the current first enters it passes round the long path through the P coil 

 and F is magnetised. The spring is now pulled down and makes a shorting contact 

 at D. The current leaves the longer path for the shorter easier one C to D, and 

 is practically excluded from P and F. The spring is released and flies back 

 restoring the long circuit, and the cycle begins anew. 



