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MR. L. N. 0. FILON ON THK KKSISTAMT. TO 



apparently general proof of this proposition. His proof, however, is subject to 

 certain restrictions which I point out, and which prevent it from being applied to the 

 sections I am dealing with. 



The sections are sensibly less useful than the circular section, their torsional rigidity 



Fig. 1. 



Fig. 2. 



Fig. 4. 



being always diminished and the maximum stress very often increased. This remark, 

 I may add, applies to all the sections dealt with in this paper. 



This usefulness or efficiency decreases as the neck of the section becomes more 

 narrow, as, indeed, might have been anticipated. 



Other sections worked out are those corresponding to angles between the 

 asymptotes of 90 (fig. 3), 60 (fig. 4), and (fig. 5) ; in the latter case the sections 

 degenerate into ordinary elliptic sections with two straight slits, or indefinitely thin 



