As for the relative rigidities of these two structures, there is very little doubt that a comparison of the finished bridges under load would result in favor of the simple span.

In making the preliminary study for the arch bridge herein

referred to, there was prepared a comparative design for a three-hinged arch, in which each half of each arch consists of a lenticular truss as shown in Fig. 6.

Contrary to the author's surmise, this design did not prove

to be any more economical than that with the circular arch. the total weights of metal in the two structures being almost