Each anchor-arm is 840 ft. long, and is divided into seven double panels, and there are seven and five-eighths loads to be considered; consequently the weight of trusses and laterals therefor will be

0.75W + 1.75W + 2.10W + 2.50W + 3.00W + 3.75W + 4.75W

+ 5/8 X 5.65W = 22.13W = 38,351,000 lbs.

This weight must be reduced, owing to the fact that the length of the cantilever arm is only six sevenths of that of the anchor-arm, making r = 0.857.

The total weight by the curves for the two cantilever and anchor-arms is therefore

2(24,090,000 + 35,609,000) = 119,398,000 lbs.

The total weight of metal given in the published estimate for trusses and laterals for the two cantilever and anchor arms, after deducting 11,500,000 lbs. for weight of metal in the anchorages and ignoring the allowance for sundries (which was probably put in for prudential reasons), is 119,700,000 lbs., making the difference 302,000 lbs., or about one quarter of one per cent.

This is an extremely accurate check, and proves that the curves are reliable; nevertheless the author would not guarantee them to give any such close coincidence for all cases.

Since these pages went to press the author has been engaged on the making of a preliminary design with a detailed estimate of weight of metal for a proposed double-track railway and highway cantilever bridge, with a central opening of 1,600 ft., to cross the St. Lawrence River near Quebec, Canada. The result of the estimate as far as it has been carried gives another excellent check on the accuracy of one of the curves; as the error for the cantilever arms is only one-eighth of one per cent. The anchor arms have not yet been detailed.