878 REPORT — 1887. 



Maximum work is done in the circuit if the electromotive force of self-induction 

 equals the electromotive force necessary to overcome the inert resistance. 



In case the circuit contain a source of counter electromotive force, such for 

 instance as a series wound, continuous ciu-rent motor, with well-laminated field, 

 excited to a low degree of magnetisation, the same reasoning applies. For the 

 counter electromotive force is in this case proportional to the current, and therefore 

 of the same character and period as the electromotive force necessary to overcome 

 the inert resistance — g =("»• + K~)I 



where K is a coefficient depending on the constructive data of the machine, and on 

 its speed, but not depending on its self-induction and periodic time. In a good 

 motor r must be small as compared with K, and therefore the approximate con- 

 dition to obtain maximum work is that the counter electromotive force developed 

 in the armature should equal the electromotive force of self-induction. In this 

 case the plant efficiency is about 71 per cent. 



Motors as usually constructed, and running at moderate speed, do, however, 

 not fulfil this condition, the electromotive force of self-induction being far too 

 high. Improvements are necessary ia the direction of reducing the self-induction, 

 and at the same time increasing the counter electromotive force of these machines. 



6. Distribution by Transformers and Alternate Current Machines. 

 By C. H. W. Biggs and W. H. Snell. 



The authors noticed the frequency in industrial applications of science of 

 results, which in the initial stages were indirect, becoming direct and of the 

 greatest importance. The leading requirements of a general system of electrical 

 distribution are well known, and may be considered under the heads of economy, 

 safety, and availability. Considerations of economy require high potential in the 

 mains, while safety requires a low potential at the point of use. The authors 

 considered the advantages and disadvantages of the various S3'stems in use, and 

 concluded that in the immediate future the best prospect of economic and safe 

 distribution was in the use of transformers, with constant cui'reut in the mains. 

 When Gauland and Gibbs first introduced the system they used constant current, 

 but could not overcome the practical difficulties of the case. Subsequently 

 Messrs. Snell and Kent suggested a method of overcoming the difficulties, but 

 found that the same device had previously been suggested by Elihu Thomson in 

 America. This device utilises from -5 to 1 per cent, of the current, and as far as 

 experiments yet show with almost perfect regulation. Several other schemes of 

 regulation have been devised, and the authors contended that, if the devices 

 were as stated by the inventors, the method of distribution should revert back to 

 the constant current, in preference at all points to the constant potential. The use 

 of transformers, it was pointed out, would lead to a renewed use of alternate 

 current machines, which would probably be in the future constructed on the lines 

 indicated. 



7. The Telemeter System. By F. R. Upton. 



The author explains that the 'Telemeter System,' invented by C. L. Clarke of 

 New York, is a method by which the slow movement of a revolving hand of any 

 indicating instrument may be reproduced by the movement of a similar hand at a 

 distant place, using electricity to convey the impulse. 



The primary hand moves until it makes electrical contact, thus sending an 

 impulse. It is here that all previous methods have failed. This contact should be 

 absolute and positive, for if it is not, the receiver will not work in unison. The 

 contact could often be doubled by the jarring of the instrument, thus making the 

 receiver jump twice. 



Clarke has overcome this defect by so arranging his mechanism that the faintest 

 contact in the primary instrument closes two platinum points in multiple arc with 

 it, thus making a firm and positive contact, which is not disturbed by any jar on 

 the primary contact. This gives the instruments a positive start for the series of 



