steel erected could be obtained for 6.3¢ per lb. What are the economics of the case? Here we have

r = 13.8 ÷ 6.3

r' = 35 ÷ 75

and r r'= 13.8/6.3 X 35/75 = 1.02

Fig. 5b gives 1.02 as the limit, which shows that the costs of structure are alike for the two steels.

In Figs. 5a and 5b the basis of comparison is standard carbon steel, and the curves were plotted from weights figured for spans actually computed and proportioned. The estimates referred to were those worked out by the author a number of years ago for his two papers, "Nickel Steel for Bridges" and its sequel, "The Possibilities in Bridge Construction by the Use of High Alloy Steels," published by the American Society of Civil Engineers in 1909 and 1915.