438 EEroET — 1878. 



FRIDAY, AUGUST 16, 1878. 



The following Papers were read : — 



1. Re-port of Committee on the Oscillation-Frequencies of the Bays of the 

 Solar Spectrum. By G. Johnstone Stoney. — See Reports, p. 37. 



2. General Results of some Recent Experiments upon the Co-efficient of 

 Friction between Surfaces Moving at High Velocities. By Douglas 

 Galtok, C.B., D.C.L., F.R.S., Sfc. 



The author of this paper has heeu recently engaged in making some experiments 

 upon the co-efficient of friction when the surfaces in contact move at high veloci- 

 ties, in connection with the action of brakes in use on railways ; and the results 

 which have been arrived at appear to present some interesting features in respect 

 of the laws which govern the co-efficient of friction. 



The experiments were made to ascertain the friction between the brake blocks 

 and the wheels of a railway carriage. 



The levers which move the brake blocks w-ere fitted with dynamometers to show 

 first, the pressure which was applied to force the blocks against the wheel; and 

 secondly, the force or tangential strain exerted between the wheel and the block 

 when the latter is pressed against the wheel. 



The dynamometers used were adaptations of Richards' indicators, which act by 

 water pressure, which transfers the pressure to cylinders fitted with pistons to 

 which a pencil is attached, so as to register the pressure over a travelling sheet of 

 paper, as is used with steam indicator diagrams. A dynamometer on a similar 

 principle was attached to the draw bar so as to register the force exerted during- 

 the experiment in drawing the carriage. 



The speed was also recorded on the diagram by means of the Westinghouse 

 speed indicator, which also acts by water pressure, and depends for its action on 

 the speed of revolution of the axles. 



The carriage or van fitted with the apparatus had two pairs of wheels — one 

 pair of wheels was fitted with brakes, whilst the other pair was free. A speed 

 indicator was attached to each pair of wheels, so that the speed of the carriage 

 could be ascertained at any time, independently of the speed of the braked wheels. 



To check the Westinghouse speed iudicator, two of Stroudley's speed indicators 

 were also attached to the van ; but these do not register automatically. 



The distribution of the weight of the van between the two pairs of wheels 

 was obtained, as well as the weight of the wheels and axles themselves. 



In order to ascertain the weight thrown on the braked wheels during the pro- 

 gress of the experiment, a dynamometer fitted to the springs of the van showed 

 the weight at every moment carried on the unbraked wheels, from which informa- 

 tion it was easy to deduce the weight on the braked wheels. 



The apparatus was designed by Mr. Westinghouse, and constructed under his 

 supervision by the Brighton Railway Company,. through whose assistance these 

 experiments were carried into effect. 



The effect of applying the brake to the wheels is twofold. So long as the 



