168

STRENGTH OK KAILS.

The reason of the variation, in the mode ofsubjecting the bar to the strain, was to ascer-tain the difference in strength between railsmerely laid upon, and those fastened to, thesupports. The superiority is in favor of thosefastened to the supports, which shews theadvantage of long bars, and, consequently,of forming the malleable iron-rails into longlengths.

The limit of permanent elasticity, in thiskind of malleable iron-rail, appears to beabout six tons ; but, when loaded with thisweight, the deflection, in the middle, amount-ed to nearly half an inch. This rail is madeto carry the same load as the cast-iron railspreviously described ; the extent of the strainby the carriages will, therefore, be two tons,which will produce a deflexion of about one-ninth or one-tenth of an inch.

The limit of permanent elasticity in this rail,as will be observed, is nearly equal to the limitof absolute strength in the cast iron ; but theformer, from the nature of the material, maybe loaded much nearer the limit of its perma-nent elasticity than the latter may, with regardto its greatest strength.