278 Electric Oscillations in Straight Wires and Solenoids. 



along tie solenoid AB when resonance is obtained with a 

 wave of 231 metres length, n = 5. The numbers indicate 

 the distances in centimetres. 



Efr. 4. 



A closer agreement between the calculated and observed 

 figures would be obtained by taking these determinations 

 into consideration. In the calculations from which the 

 wave-length 217 was derived, the value for h substituted in 

 equation (12) for n = 5 was 2//5 = 91 centimetres, whereas 

 the length P 2 P 4 at the centre of the solenoid is 99 centi- 

 metres. If this value had been taken for h the wave-length 

 would have been 230 metres, which is very near the value 

 given by the wave-meter. 



It appears from these considerations that there is no simple 

 relation between the frequencies of the free oscillations of a 

 solenoid. 



11. A complete series of free oscillations of a solenoid may 

 be obtained by using two similar inducing coils which are 

 connected in parallel and form part of the oscillatory circuit 

 connected to the valve. 



The coils are placed near the ends, and by means of 

 a reversing key the connexions may be altered so that the 

 currents in the two coils may be either in the same or in 

 opposite directions. In the modes of oscillation corre- 

 sponding to the odd numbers the currents in the solenoid 

 are in the same direction in sections near the ends, and these 

 oscillations are obtained when the currents in the inducing 

 coils are in the same direction. In the modes corresponding 

 to the even numbers the currents in the sections near the 

 ends are in opposite directions, and these are obtained by 

 changing the connexions of one of the inducing coils by 

 means of the reversing key. 



The inducing coils affect the capacity of the solenoid, but 

 the method has the advantage of giving a symmetrical distri- 

 bution of current on either side of the centre of the solenoid 

 for both the odd and even series of free oscillations. 



