It is possible that the author is not entirely justified in making this surmise, because computations might show that the span length for equal cost does not exceed 2,700 feet, no matter how high may be the alloy of steel used. It seemed hardly worth while to spend much time in figuring

upon this question before a high alloy of steel satisfactory for long-span-bridge building is found; nevertheless, as a matter of curiosity, it was decided to test a main span length of 2,900 feet, for steel having an elastic limit of 80,000 pounds per square inch, and assuming that the cost of that metal in place is 9 cents per pound.