steel which should be used in a nickel-steel span depend upon the ratio of unit costs and that of elastic limits, and are not constant. Thus, if the excess unit cost of nickel steel were large, it might pay to employ carbon

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steel in the floor system, and even in the posts; while if the said excess were small, it might be economical to use the alloy in those parts. The author's reply to this criticism is that his experience in figuring with alloy