758 Sir Oliver Lodge on 



other to excite a third, and so on. By this means it was 

 clearly perceived that the frequency could be made to mount 

 up in arithmetical progression with the number of machines. 

 But the obvious cumbersomeness and wastefulness of the 

 arrangement, although it was true that all the dynamos 

 might run on the same shaft, caused the idea to be promptly 

 abandoned. 



Dr. Goldschmidt, however, has now made the interesting 

 discovery that all these steps can be taken in a single 

 machine, with some manifest and some unexpected ad- 

 vantages, and apparently with sufficient economy for 

 practical purposes even at high power, so long as the final 

 frequency does not exceed say 50,000 per second. 



The fact that iron is used, and to all appearances 

 necessarily used, in attaining this result, although its 

 magnetization should not be pushed beyond a permeability 

 of 100 or something below the steep part of a magnetization 

 curve, necessitates many instrumental precautions, much 

 careful design, and considerable constructive skill ; but 

 designers of the Firm of Messrs. C. Lorenz, and Engineers 

 of the Firm of Messrs. Bergmann, both in Berlin, have been 

 able to execute machines which certainly work in the way 

 expected. 



So far as I am aware Physicists in this country have 

 not made themselves generally acquainted with the device 

 employed, and inasmuch as its ingenuity commands ad- 

 miration, I venture 



(1) to expound the principle briefly, 



(2) to attempt a theory. 



The features of the machine and the laws utilised may 

 be all considered known when taken separately, some of 

 them well known ; and yet, in combination, they work in a 

 way which at first sight seems puzzling and might readily 

 have been pronounced fanciful. 



The separate points on which the invention is based may 

 be thus stated : — 



(1) That when the field magnet of an alternating dynamo, 

 with a number of poles distributed round a circle, is itself 

 excited by an alternating current, its field may be considered 

 as revolving equally in two opposite directions ; i. e., its 

 magnetism revolves although the iron is mechanically 

 stationary. This is merely because each North pole changes 

 sinuously into a South pole, and each South pole into a 

 North ; thus virtually changing places in a continuous 

 cyclical manner. 



