The New York Rapid-transit Subway

Proceedings.] CORRESPONDENCE ON NEW YORK SUBWAY. 133 by the formula given in the Paper, appeared to agree generally Mr. Waring, with that obtained by the usual formulas. Mr. Waring attached considerable value to the use of transition-curves, as enabling the superelevation of the outer rail to be gradually run out inversely to the radius of the curves, as it should be; but it was manifest that on mountain railways, where the use of reverse curves of the minimum radius permissible, with very short pieces of straight line between them, was often imperatively necessary, either from local conditions, or from the necessity of keeping down the cost of the work, the use of such transition-curves was impracticable. Mr. Waring was much interested in learning, from the results of the experiments described on pp. 45 and 46, that cement concrete broken up 24 hours after mixing and retempered would acquire an ultimate strength in excess of that of the same concrete left undisturbed, as this was quite contrary to the general experience of English engineers. Perhaps the Author could give some further information as to what this process of retempering was ; but if, as Mr. Waring supposed, it meant merely working up again the partially-set concrete with only the addition of a little water, he thought the results obtained were very surprising. The Author, in reply upon the Correspondence, observed that The Author, reference had been made to the platforms and columns. In practice columns set near the platform edge had not been of serious incon- venience, as the car-doors did not swing outwards, and trains were started by bell-cord signal and not by hand from the platform. It was better, of course, to omit platform columns, but this could not be done always. Passengers were not allowed to enter or leave by the end doors of the train, so that the length of the train could exceed that of the platforms.