pieces of angle or plate for staying same are not to be used, for better results are obtained by placing the angles in the form of a T.

18. In all main members having an excess of section above that called for by the greatest combination of stresses, the entire detailing is to be proportioned to correspond with the utmost working capacity of the member, and not merely for the greatest total stress to which it may be subjected. In this connection, though, the reduced capacity of single angles connected by one leg only must not be forgotten.

19. Designs must invariably be made so that all metal-work after erection shall be accessible to the paint-brush, excepting, of course, those surfaces which are in contact with each other or with the masonry. This requirement rules out all closed columns of every type and description.

20. In general, details must always be proportioned to resist every direct and indirect stress that may ever come upon them under any probable circumstances, without subjecting any portion of their material to a stress greater than the legitimate corresponding working-stress.

21. In all designs simplicity in both main members and details is to be considered of the greatest importance.

22. In all structures rigidity is to be considered quite as important an element as mere strength.

23. Structures on skews are to be avoided whenever it is practicable to do so.

24. The use of more than a single system of cancellation in bridges shall be confined entirely to lateral systems and swaybracing, except that at mid-panels of trusses two rigid diagonals connected at their intersection may for appearance be employed, provided that either diagonal have sufficient strength to carry the entire shear in either tension or compression, and that the adjacent vertical posts be figured accordingly.

25. The use of redundant members in structures shall not be allowed, excepting only in the case just mentioned of rigid mid panel diagonals.

26. In all designing true economy must be given the utmost