STRENGTH OF RAILS,

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previously given the opinion of some engineerson the comparative merits of cast and mallea-ble iron-rails; there is, however, a great dealyet wanting, in a practical point of view,more than mere opinion. There are wantingexperiments to prove the different properties—their strength, durability, and the resistanceto the carriages moved along them. It hasbeen my wish to supply that defect, so far asthe opportunities within my reach have ena-bled me; I regret to say, however, that myinvestigations have, as yet, not reached beyondthe first, at least in the shape of experiment.The ultimate wear will require time to eluci-date ; and I have not yet had an opportunityof ascertaining the comparative resistance ofcarriages moved along them. I shall, there-fore, at present confine myself to their relativestrength, as ascertained by experiments.

The most general form of the edge-rail isthat of a parabola on the under side, theupper side being quite straight. The atten-tion of mathematicians has not been muchoccupied in this particular case, or in demon-strating the strongest form of section when theweight is rolled along the surface. Whenthe beam is supported at each end, as is thecase with a rail, and loaded in the middle,