ON GRAPHIC METHODS IN MECHANICAL SCIENCE. 327 



by the fact tliat wlicn the machine yields its best permanent electric oat- 

 put the magnetic resistances of the iron and the air space are equal. To 

 iiud this point it is only necessary to fix the value of the magnetic field 

 at which it is desired to work the dynamo. The upper part of the curve 

 is then drawn to coincide with that particular Frohlich's curve of mag- 

 netisation (a hyperbola) which passes through the point found above and 

 a point on the straight line, previously found, corresponding to a field of 

 10,000 units (C.G.S). The passage from the straight line to the Frohlich 

 curve is drawn by hand. 



The authors state that such a curve suffices for solving all ordinary 

 problems connected with the proposed dynamo, but it is scarcely accurate 

 enough to apply to such questions as relate to the compounding of the 

 coils of the machine and the regulation of its current. These, in general, 

 must be left alone until the machine is constructed and an experimental 

 characteristic determined. 



(2) In connection with alternate current work, Blakesley ' has published 

 some very interesting graphical solutions of questions relating to self- 

 induction, mutual induction, and capacity ; but, as they refer only to the 

 case in which the electromotive force is a simple sine function of the time, 

 they have not been used in practical work. They depend upon the fact 

 that the counter-electromotive forces acting in a circuit, set up by self- 

 induction or mutual induction, and opposing an original harmonically 

 varying electromotive force, themselves vary harmonically, and have the 

 same period as the original electromotive fotce. Consequently the effec- 

 tive electromotive force in the circuit at any moment can be found by 

 combining all the separate E.M.F.'s by the parallelogram law as applied 

 to simple harmonic motions in general. Although the case considered is 

 never realised in practice, some dynamos very approximately fulfil the 

 conditions, and the author has ventured to extend the solutions to the case 

 of the transmission of power by alternating currents and the determina- 

 tion of the conditions under which the maximum efficiency is obtainable. 



Report of the Committee, consisting of Sir J. N. Douglass, Pro- 

 fessor W. C. UmviN {Secretary), Professor Osborne Reynolds, 

 and Messrs. W. Topley, E. Leader Williams, W. Shelford, 

 G. F. Deacon, A. K, Hunt, and W. H. Wheeler, appointed to 

 investigate the Action of Waves and Currents on the Beds and 

 Foreshores of Estuaries by means of Working Models. 



[Plates I.-IX.] 



The Committee held their first meeting in the Central Institution of the 

 City and Guilds of London Institute. It was then resolved that the 

 Committee should avail themselves of the permission of the Council of the 

 Owens College, and conduct their experiments in the Whitworth Engineer- 

 ing Laboratory. 



At the suggestion of Professor Reynolds it was arranged that the first 

 experiments should be directed to determine in what respects, and to 

 what extent, the distribution of sand in the beds of model estuaries of 



' Blakesley, Electrician, 1885, passim ; reprinted in book-form in Electrician series 

 Also Phyi. Soc. Journal, ix. p. 85 (Jan. 1888). 



