special tool for cutting the webs to a circular curve, but after this was made, the manufacture was easy and comparatively inexpensive.

In Engineering News of May 20, 1915, there appeared an excellent article by Mr. Maurice E. Griest, Assistant Designing Engineer of the Public Service Commission of New York City, entitled "Design of Steel Elevated Railways, New York Rapid Transit System," in which he gives a diagram showing that for structures located in the street the economic span-length is fifty feet, but that for lengths from forty-five feet to fifty-five feet there is not much difference in the cost. This not only confirms the author's findings of two decades earlier, but also is in accordance with a general deduction made by him of late from several economic investigations, viz., that, up to a certain limit, a material variation from absolutely economic conditions can generally be made without seriously increasing the total cost, but when the said limit is passed the uneconomics involved increases rapidly.

For further information concerning the details of elevated railroads, the reader is referred to the before-mentioned "Transactions" of the American Society of Civil Engineers.