Coefficient of Coupling of Oscillation Transformers. 7(>3 



We can therefore construct a rectangular circuit of wire 

 attached to the lid of the hox of the cymometer, which has 

 a known predetermined inductance of say 5000 centims. 

 Strictly speaking there is a small correction for the tails of 

 parallel wire which connect the rectangle to the jar at one 

 end and to the coil at the other. If considered necessary, 

 this may be taken into account by employing a reduced case 

 of the above formula for the inductance of the rectangle. 

 If there be a pair of round wires of diameter d placed at a 

 distance D apart, the inductance for a length I of the parallel 

 wires is given by the formula 



I/=«(log 2 ^) (2) 



Hence, if the length of the tails of wire at each end of the 

 rectangle is the same and equal to /, the inductance of the 

 whole circuit is equal to 1^+21/, where L x and 1/ have the 

 values given by the formuke above. 



If we wish to determine the high frequency inductance of 

 a short length of wire, say a loop of copper wire of one or 

 two turns, we proceed as follows : — We insert this loop in 

 series with the rectangular circuit and with a condenser 

 of which the capacity has been determined, and employ the 

 cymometer as above described to determine the oscillation 

 constant of the circuit. Then let L 2 be the inductance of 

 the loop of wire, and L, that of the rectangle, and (X the 

 observed oscillation constant when L^ is used alone, and 

 2 when L x and L 2 are in series. Then we have 



O^CLj 



2 2 =C(L 1 + L 2 ); 



whence T 2 2 -CV 



We can always check the result by using as a loop some 

 form of circuit, of which the inductance can be calculated. 



Thus if we bend a bare round-sectioned copper wire into 

 a square with the ends brought quite near together, we can 

 predetermine its inductance. 



We have here a reduced case of the general formula for a 

 rectangular circuit. In equation (1) above put S = 8' and 

 put 1$ = /, then the formula reduces to 



L= 21 (log J -2-853) (?,) 



