Alternators in Parallel. 309 



owners of various high-frequency machines kindly furnished 

 the author with data of their alternators. These data are 

 collected in Table II. (pp, 306-7) together with three more 

 recent alternators. The writer hopes that a description of 

 other machines may be forthcoming in the discussion on the 

 present paper. 



In conclusion the author would like to point out that he 

 has described this machine not with a view of suggesting it 

 as the best, or even as a satisfactory, design, but rather to 

 indicate some of the difficulties which are encountered in 

 attempting to construct an alternator for high frequencies. 

 The machine served its purpose and allowed the research for 

 which it was designed to be completed, and no further work 

 has been done on it, though there are several very obvious 

 improvements which would greatly increase its output and 

 utility. Firstly, the greater part of the difficulties were 

 encountered with the belt-drive and the bearings, these could 

 obviously be got over by mounting the inductor direct on the 

 shaft of a steam turbine. A larger inductor, say 10 to 15 cm. 

 diameter, could also probably be used with 200 teeth and a 

 speed of 30,000 r. p.m. to give 100,000^ per second. Secondly, 

 the lamination of the iron must be carried to a very high degree 

 to prevent eddy-current losses, and the armature-coils must 

 be fixed as near as possible to the very tips of the poles. 

 Thirdly, with accurately-spaced teeth on the inductor a large 

 number of armature poles could be used. 



All the experiments described in this communication were 

 carried out at the Central Technical College. The author 

 wishes to express his indebtedness to Prof. Ayrton and 

 Mr. Mather for much valuable assistance and advice. 



P IJi 



XXXI. Alternators in Parallel. 

 By Captain E. Henderson, Royal Marine Artillery*. 



THE recent investigation by Professor B. Hopkinson on 

 the conditions causing u Hunting in alternators " have 

 re-directed interest to the older analytical treatment by Dr. 

 John Hopkinson of the coupling of alternators in parallel. 

 In Perry's ' Calculus for Engineers ' this problem is treated 

 in a very concise manner, owing to his symbolical modifica- 

 tion of the complicated mathematics once thought necessary. 

 It may be advisable to point out that there are slight 

 algebraical omissions in the results given by Professor Perry 

 on page 261 of the 'Calculus for Engineers'; the work 



* Communicated by Prof. A. G. Greenhill, F.R.S. 



