the Goldschmidt Dynamo. 761 



(8) The current and the E.M.F will be in the same 

 phase, and lag will be obliterated, if the precise frequency 

 is maintained. 



(9) The system is not self-exciting but requires an initial 

 starting current or an excited magnet, without which the 

 whole is inactive. The initial current supplies no energy 

 however, and, if no variations were wanted, its place might 

 be taken by a permanent magnet. All the effective energy 

 of the system is derived from the mechanical rotation ; 

 and signalling can be managed by varying the exciting 

 current. 



(10) The original exciter may be either a steady current 

 or a comparatively slowly alternating one, say of acoustic 

 frequency. It might for instance be supplied through a 

 microphone and be carved into fluctuations by speech, which 

 could thus apparently be effectively magnified and indirectly 

 transmitted to a distance. The frequency of the exciting 

 stimulus is of no consequence so long as it is incomparably 

 slower than any of the really high frequencies to which the 

 circuits are tuned. 



An exciting current of acoustic frequency, say 500 a second, 

 is practically a steady stimulus of slowly varying strength 

 during each half period ; but the result of employing such a 

 current as the stimulus may be the powerful emission of a 

 note of .1000 per second, when the perfectly inaudible electric 

 waves are collected and reinterpreted by some device. 



(11) The neutralisation of self-induction by capacity 

 applies not only to the whole of a circuit but to any part of 

 it for which the condition corresponding to p 2 LS = l is 

 satisfied ; and the only obstacle in that part of a circuit is 

 then its ohmic resistance, subject of course to any throttling 

 or skin effect due to the most favourable automatic distribu- 

 tion of current in the substance of the conductor ; a distri- 

 bution which can be made virtually uniform by adequate 

 subdivision, as by employing a cable composed of fine 

 insulated wires. In so far as iron is used, the resistance 

 term will contain eddy-current losses and hysteresis, which 

 must be guarded against in known ways. 



(12) That if to a circuit with one L and S in series, 

 another L and S pair is added also in series, the natural 

 frequency is unaltered; for though the resulting inductance 

 is doubled, the resulting capacity is halved, and the product 

 remains the same. The advantage of such a doubly-tuned 

 circuit is that its parts are connected by nodes, to which 

 anything can be attached without disturbance ; for a pair of 



