TRANSACTIONS OF SECTION 0. 741 



3. The Design of Transformers} By J, Swinburne. 



The present practice in designing transformers is to use a continuous or closed 

 circuit for the core, and to make this core very large in cross-section, so that the 

 excitation needed to produce the desired induction is small. The tendency is, 

 in fact, to increase the quantity of iron in a transformer, and to decrease the 

 copper. 



The excitation in a closed circuit transformer is a matter of little importance, 

 but the loss of power by hysteresis may be, and often is, very serious, especially 

 when it is remembered that transformers used in houses have their full load on only 

 very occasionally, while the loss by reversal is going on continuously. The author 

 Las calculated tables showing the best forms that can be given to closed circuit 

 transformers for various loads, the loads being on for ditVerent numbers of hours 

 per day. These tables show that, even for cases where the full load is always on, 

 the cores should be smaller than is now usual ; and that for most house work, when 

 the transformer is only at times partially loaded, the cores ought to be exceed- 

 ingly small to give a high efiiciency, and that the high efficiency is accompanied by 

 excessive variation of secondary electro-motive force and high cost. 



Open circuit transformers of the type introduced by tlie author can be made, 

 in which even the full-load elliciency is higher than can be got with a closed 

 circuit, while the very low average efficiency of house- transformers can be remedied 

 without great variations of secondary pressure or heavy cost. 



The author's transformer is of the Ruhmkorff coil type, but has the core brought 

 out past the ends of the copper coils, and the wires spread out into a sort of thistle- 

 head or hedgehog. The induction is not great at any region in the air, and the 

 magnetising current is not large enough to balance the advantage of the small 

 volume of iron needed. 



4. Electric Launches on the Thames."^ By G. Forbes, F.B.8. 



This paper has arisen out of the fact that during the past summer, while the 

 author was living on the banks of tlie Thames, he took the opportunity to keep one 

 of the electric launches which have lately been built by Mr. Tagg and electrically 

 equipped by Messrs. Immiscli. There are certain peculiarities about the Thames 

 wnich render the wants of a launch-owner somewhat diderent from what they may 

 be on other waters. The author thinks it well to make known his experiences, in 

 order to hasten what lie considers must be an accomplished fact ere many years, 

 viz., the extinguishing of pleasure steam launches from the river Thames owing to 

 the survival of the fittest. 



Among the points worthy of notice are that launches are chiefly wanted in 

 summer, wiien the heat and smoke, smell, oil, and dirt of a steam launch are 

 objectionable, and that owing to the large traffic, and to prevent injury to the 

 banks and boats on the banks it is impossible to allow high speeds in launches; 

 hence, a comparatively small supply of accumulators or storage batteries is required. 

 It may also be added that on the Thames it is easy to secure a sufficient number of 

 charging stations. At present there are four or five at easy distances apart. 

 Eventually the hotels on the river will be lighted electrically, and this power can 

 be used for charging the storage batteries on launches. The author's house was at 

 Bray, and each night after dinner he sent the launch or took it up, towing a boat 

 for the return journey, to a charging station a mile away, just above Boulter's Lock. 

 At breakfast time the ' Delta ' was always found moored in front of the house. A 

 start was generally made after breakfast, and on returning to dinner at 8 p.m. the 

 charge was never exhausted. The boat could be easily managed by a lady, even 

 when entering and leaving crowded locks. 



The ' Delta' is '.M>, feet in length, and has a beam of feet, her draught is 15 

 inches forward and 18 inches at the stern. She is fitted with 44 cells, weighing in 

 all 2,520 lbs. She is steered by a wheel in front within reach of the three handles 



' Printed in extenso in the Electrical liericw for September 20, 1S89. 

 ^ See Electrician, vol. xxiii. p. 504. 



