

Oscillations in Straight Wires and Solenoids. 269 



generator or by altering the capacity of the condenser C pro- 

 vided one position of resonance of the bridge is well within a 

 quarter of a wave-length of the ends Y : Y 2 . It was also 

 found that the wires need not be accurately parallel, as the 

 length of a wave as found with wires 5 centimetres apart at 

 one end and 5*2 centimetres at the other end was the same as 

 when the wires were 5 centimetres apart at both ends. 



5. In order to measure waves which are long compared 

 with the length of the wires, a circuit consisting of an 

 ordinary inductance with tappings and a variable condenser 

 of about one millimicrofarad was maintained in oscillation 

 by a valve. The reactance was made much higher than that 

 required for starting oscillations, in order that the harmonics 

 should be well developed. 



With an oscillatory current of about 2 amperes in the 

 generator ti.e first ten harmonics were easily observed 

 directly by a wave-meter, using a thermo- junction to detect 

 the current, and frequencies were exactly proportional to the 

 numbers 1, 2, 3, 4, etc. The wave-meter had been carefully 

 adjusted to the National Physical Laboratory standards, and 

 changes of one per cent in wave-length were easily observed. 



The higher harmonics of the long-wave generator may be 

 measured by the beats obtained by combining them with 

 oscillations induced by the short-wave generator. These 

 beats are easily observed by inserting a telephone-transformer 

 in. the anode circuit of the long- wave generator, and making 

 the grid connexion in the latter circuit with a wire which 

 passes near the short-wave generator. The beats thus pro- 

 duced in the telephones are sufficiently strong to be easily 

 heard without tuning the anode connexion of the long-wave 

 generator to the frequency of the short-wave generator. 



If iv be the wave-length of the fundamental oscillation of 

 the short-wave generator, W that of the long- wave generator, 

 then W is an exact multiple of iv when one of the harmonics 

 is iu tune with the short-wave generator. When W is fixed, 

 and the wave-length of the short-wave generator varied con- 

 tinuoisly, a series of m harmonics come into tune as w 

 passes from the value w Y to w 2 . The number m may thus be 

 counted and the following relations between the wave-lengths 

 are obtained : 



W = nw 1 — (71 + m) w 2 . 



Thus ~\\ T = mw l ic 2 /(w l — iv 2 ). 



The first and last oscillations of the series ir { and ic : are 

 accurately adjusted to resonance with harmonics and their 

 lengths determined by means of the parallel wires. It will 



