220 KEPORT— 1869; 



When applied as a marine boiler, the advantages of this plan are very great, re- 

 quiring only a very small cubic space compared with the heaiing-sm-face. Finally, 

 the very good results obtained from boilers made according to this invention have 

 fully realized the most sanguine expectations formed of its merits. 



On a Method of determining the true amount of Evaporation from a Water- 

 Surface. By G. J. Syjions, F.M.S., and E-ogeks Field. 



[For Abstract of this Paper, see Section A, page 25.] 



Railway Passengers^ and Guards^ Communication. 

 By S. Alfred Vaeley, Assoc. Inst. C.E. 



The author remarked that the subject had occupied considerable attention, that 

 he had been engaged upon it during the last four years, and he thought there would 

 be some points of interest in a description of a system of communication which was 

 applied in 18(36, and is at the present time in use on the Eoyal train in which Iler 

 Majesty travels to and from the A'orth ; tiie s}-stem referred to had also been applied 

 to an ordinary train, and daily used for more than eighteen months. 



The author stated there was a belief on the part of some (but by no means all of 

 the railway authorities) that, owing to the subtle nature of electricity, it was not 

 suitable for the purpose of train intercommunication ; but he thought this belief 

 arose chiefly from a want of acquaintance with the progress made by those who 

 have made the practical application of electricity their special study, and he believed 

 the time would come wlien electricity would be imiversally acknowledged to be 

 the best medium for signalling upon the rolling-stock of this country. 



The author remarked the application of electricity to signalling in trains, con- 

 sidered in the abstract as an electrical problem, was a sim)ile one ; the mechanical 

 difficulties in its application, however, had been somewhat complex, and the solution 

 of these difficulties had depended chiefly upon the mechanical construction of the 

 various parts. 



The conditions laid down by the railway authorities as necessary, were that the 

 system should be simple and not liable to derangement, that passengers should be 

 able easily to signal in an emergency, and that the apparatus should be detective 

 to prevent the repudiation of a signal when once given ; besides this it was suggested, 

 for the sake of economy, that the apparatus should be portable, so that it could bo 

 moved from one train to another if required. 



Numerous electrical systems had been proposed, but only three had been practically 

 applied. 



The first on the list was Mr. Preece's, in use on the Lundon and South- Western 

 Railway ; the second was Jlr. C. Y. Walker's, in use on the South-Eastcrn Railway ; 

 the third the joint invention of JNIr. JNIartin and Mr. S. A. Varley, and in use upon 

 the London and North-Western Railway. 



The three systems referred to differed from one another in the mechanical con- 

 struction of the couplings, the alarums, the galvanic batteries, and the carriage 

 signalling apparatus ; he did not, however, propose to discuss their respective merits, 

 butwould couttne himself to adeseription of the system with which he was associated. 



An insulated wire was run underneath the carriages, the coupling bars and iron- 

 work of the carriages were connected electrically together, and the circuit was com- 

 pleted, when the apparatus was in use, through the insulated wire, the apparatus, 

 the ironwork, and tlie railway metals. 



Two insulated wires, the one connected to the ironwork, the other to the insulated 

 wire running under the vehicles, were led up into the compartments of each carriage, 

 and bringing these into contact with one another closed the circuit through the 

 galvanic batteries and the alarums in the vans, and on the engine. 



The connexions between vehicle and vehicle composing the train were effected 

 by means of two coupling-ropes containing flexible conductors ; this enabled the 

 can-iages to be joined together at either end, and gave a double connexion between 

 *ach vehicle. 



The coupling-ropes were made by wrapping a wire spirally round a hempen core ; 



