TKANSACTIONS OF SECTION G. 773 



motor as a great advance over the Tesla macliine. The only advantage which it 

 possesses over sjnchroiiising alternators without iron in the armatures and with 

 large momentum, lies in its power to start with the load on. ]3ut I do not see 

 that in large applications this advantage is to he compared with what it loses by- 

 its want of synchronism. M. Dohrowolski claims that these machines have the 

 further advantage over the synchronisers that they will not stop when overloaded. 

 After having tested Mr. Mordey's synchronising alternators, 1 have a strong con- 

 viction, almost amounting to a feeling of certainty, that it is impossible to put 

 them out of step in ordinary conditions by merely increasing the load. The more 

 you increase the load the more current goes through them to keep them in step. 

 They would rather get red hot than get out of step. They behave just as a con- 

 tinuous current motor or Tesla motor, or a Dohrowolski motor, behaves under the 

 same conditions ; it gets hot, but it does not stop. 



People seem to be greatly at a loss to explain why it is that some alternators 

 work well as motors, while others do not. The explanation is simply that the 

 former have a large momentum, and the latter have not. I announced this ex- 

 planation of the difficulty at a meeting of electricians in Paris, last February, and 

 found that M. Hospitaller had arrived at exactly the same conclusion, and quite 

 independently. I feel confident in predicting that the Ferranti dynamo, if supplied 

 with a heavy enough fly-wheel, will he found to work as well as the ^lordey 

 machine as a motor. 



4. On Electric Firedamp Indicators. Bij N. Watts. 



5. The Lighting of Railway Traivs ElectricalJij. Bij I. A. Timmis. 



The main conditions that are necessary are : — 



(1) Every carriage must carry its own store of electricity {i.e. a battery). 



This battery must be light, say less than 1 cwt. 



No carriage must be detained at any time to change its batter}-. 



(li) High voltage lamps must be used to give a brilliant light and economise 

 the current used. 



The system described in the paper can be, and is, used with — • 



(i.) A dynamo driven from an axle, or 



(ii.) A dynamo and special engine on the locomotive; 



(iii.) Central charging stations. 



In the first and last cases it is necessary to have a large battery in the guard's 

 van. 



Whatever the main source of electricity may be, it supplies the current at a 

 high voltage (say 50) to light a main system of lamps through the train. 



But as any carriage may be detached at a station to be recoupled on to another 

 train or break loose or be slipped from a train, it is absolutely necessary to have a 

 storage or battery of accumulators in each carriage. 



The cost and weight of batteries in each vehicle, with E.M.F. enough to light 

 the main lamps (say 50 volts), makes them impossible. Further than this, it would 

 be impracticable to charge them. 



We therefore put another system of small lamps, 6 or 8 volts and 3 or 4 small 

 cells, in each vehicle to light them. 



These small batteries we charge from the main source of electricity on the train, 

 and thus they are no trouble — small weight and small cost. 



The working of these two systems, main and auxiliary, is imder the control 

 of the guard while the train is complete ; but should any vehicle become detached 

 from the main circuit the auxiliary lamps automatically light up. 



If, also, anything happens to the main source of electricity, the auxiliary system 

 can be put either under the control of the guard or be fitted to come into action 

 automatically. 



The placing of the main leads through each vehicle, and the couplers used, aie 

 fully described in the paper. We sometimes use four through leads and sometime* 



