56 Dr. McLaclilan on Effective Inductance, Effective 



loss 4- copper loss) decreases, the portion due to copper loss 

 increases. These effects are more pronounced the greater the 

 coupling between the exploring coil and the primary winding. 



In the actual case of the magneto the effects are not 

 nearly so marked as those obtained with the exploring coil, 

 owing to the brass end-plates being slotted. At 10,000 — - 

 the diminution in the inductance and effective resistance 

 was o£ the order of 5 per cent, with the armature in or out 

 of housing *. The effect of the aluminium end- plates carrying 

 the outer ball races was examined, but it was extremely small. 

 The influence of the other non-magnetic fittings surrounding 

 the iron circuit was not examined owing to lack of time. It 

 will be shown later that the dielectric loss is proportionately 

 small. It is probable, therefore, that the greatest loss is due 

 to the iron, although the eddy currents in the non-magnetic 

 fittings in which the laminations are fixed must contribute to 

 the total loss. 



One method of investigating the latter source of loss would 

 be to build a magneto with the laminations held in non- 

 metal fittings, and compare the results with those obtained 

 for the standard machine. Care would have to be taken to 

 ensure small dielectric loss in the non-metal fittings. Tests 

 could be conducted with the rotor at rest or in motion. 



(e) Effective Permeability. 



The effective permeability of the complete magnetic circuit, 

 not merely the iron per se, has been defined by equation (3). 

 It is an index of the usefulness of the iron in increasing the 

 flux through the windings. The curve of fig. 16 shows the 

 variation with frequency. Its general shape is in accord- 

 ance with the deductions on pp. 35, 39. On comparison 

 with a* static permeability curve, it will be seen that /x e is 

 greatly reduced»owing to the air-gaps which are of paramount 

 importance at low frequencies. This will be clear on in- 

 spection of curves (1) and (2) of fig. 10. Since the inductances 

 decrease with increase in polarization, it is evident that fi e 

 decreases too. 



(f) Self-Capacity of Secondary winding . 



The self-capacity of the secondary was measured at fre- 

 quencies from 2 x 10 4 ~ to 7x 10 4 ~ per second by the 



* From a peak-voltage test on full advance and retard the effect of 

 the brass end-plates was negligible. If the slots in the end-plates are 

 closed, the peak-voltage is reduced considerably. 



