generated in a High-tension Magneto, 



161 



capacity Co diminishes, and the product (Li-fL^Co shows 

 little variation over a wide range. For example, with the 

 small coil the optimum was 0*0475 microfarad, and the 

 product (In + I^Co was 0*689 . 10~ 9 ; with a series in- 

 ductance of 0*00527 henry the optimum was 0*0325 mfd., 

 and (L I + L 3 )C = 0611. 10' 9 ; with L 3 = 0*0104 henry 

 Co was 00225, and (L 1 + L 3 )C = 0*5^8 . 10" 9 c.g.s. But 

 when the series inductance was omitted altogether the 

 optimum fell to below 0*02 mfd., and the product of 

 the primary self-inductance and the capacity to less than 

 0*27 . 10~ 9 . Thus a marked diminution occurs in the 

 product of primary self -inductance and optimum capacity 

 when the small series coil is omitted ; and this is precisely 

 what we should expect when the optimum changes — owing 

 to the shrinking of the first arch with increasing coupling — 

 from the first to the second arch of the curve, which change 

 occurs at about F = 0*7. That the change is from the first 

 arch to the second, and not, for example, from the second to 

 the third, is shown by the comparatively small variation in 

 the product (Lx-f-l^Co as the series inductance is largely 

 increased (cf. Phil. Mag. Aug. 1915, p. 231, Table I.) *. 



We shall therefore take 0*7 as the coupling with the small 

 auxiliary coil in the primary circuit ; and on comparing the 

 abscissae of the highest point of the first arch in figs. 5 and 6, 

 we find 



(L 1 + L 3 )Cc 

 LoCo 



= 0*465, 



Thus the product of self-inductance and capacity for the 

 secondary coil is 



T n 0*689. 10- 9 1 |fi in _ 9 

 22 = — M65 — = ' C,g,S * 



5. Measurement of the Inductances, the Coupling, and the 

 Effective Resistances by Oscillation Methods. 



When the magneto was connected with the electrostatic 

 oscillograph f it was found that, as was to be expected, no 



* It can be shown that when a series inductance L 3 is connected 



between the point J (fig. 1) and the condenser, the expression for the 



v -u L ^L 2 i (a-l)L ," .,, .. (L 1 +L 3 N )C 1 

 coupling becomes .-j — r T ~ — r-y— > and that the ratio - — ^—^ 



takes the place of u in the equations. For the purposes of the present 

 experiments, however, the effect of an auxiliary inductance in reducing 

 the coupling was determined experimentally (see Section 5 below), 

 t Phil. JVlag. Aug. 1907, p. 238. 



Phil. Mag. S. 6. Vol. 36. No. 212. Aug. 1918. M 



