38 



everyday practice, corbels can not be considered as desirable, and as 

 designed and recommended by the author of the paper there is a 

 decrease in bearing- value on the cap in place of an increase.* 



In relation to the posts, the aim of the author of the paper would be 

 evidently to scale down the posts of the different bents to such odd sizes 

 as would correspond Avith the mathematical calculations of strength. 

 For the example presented of a post about 12 feet high, the author 

 recommends a 9 by 9 inch stick in place of a 12 by 12 inch stick, or, in 

 other words, the actual size in use is about 75 per cent larger than the 

 theoretical requirements. This might seem to indicate that a similar 

 disproportion prevails for all lengths of posts. Attention should be 

 called, however, to the fact that even theoreticians would hardly desire 

 to call for a post much less than 9 by 9 inches on a trestle for support- 

 ing heavy locomotives, even for very short posts, while the longer the 

 post gets the more nearly the theoretical size will correspond to current 

 practice, which is to use practically 12 by 12 inch sticks throughout. 

 The comparatively low height of trestle assumed by the author of the 

 paper for demonstrating the case does not really represent a fair aver- 

 age of the trestles in the country as far as the proportion of theoretical 

 to actual sizes of posts is concerned. In other words, the grand aver- 

 age of actual current work would show that the timber used for posts 

 is closer to the theoretical requirements than in the example assumed 

 for illustration. 



The use of 12 by 12 inch stuff indiscriminately, while wasteful of 

 timber in certain cases, is warranted by a great many practical features 

 which absolutely control the situation and predominate far above theo- 



* The reviewer here and elsewhere has missed the main point made for the use of 

 corbels as proposed, namely, that they as well as caps and sills be of oak or some 

 similar hard wood, so that a smaller bearing area will yield twice the strength. The 

 bearing areas have been made sufficient to give a factor of safety of 3 for oak. The 

 corbels were used to give the stringers sufficient bearing area. — A. L. J. 



To this rejoinder Mr. Berg had an opportunity of replying, the reply being as 

 follows: 



"Tf corbels and caps of a trestle are made of a timber like oak, with a relatively 

 high unit resistance to crushing across grain, as suggested by Mr. Johnson, then the 

 deficient bearing at the ends of the usual stringers in practice will be obviated. It 

 is a question, however, whether in practice it would be feasible to make such a dis- 

 tinction and to utilize several species of timber. For special work the proposition 

 is all right, but for the general run of railroad work it would be difficult to introduce 

 this innovation, especially in sections of the country where hard timber for the cor- 

 bels and caps would be more costly or difficult to obtain. Practical men also claim 

 (although how correctly I am unable to say) that different species of timber in con- 

 tact with each other will rot quicker than if only one kind of timber is used, and 

 this statement has especially been made frequently in connection with bringing 

 oak timber and soft pine timber in contact with each other." — W. G. B. 



[The last objection has no physiological basis. The former illustrates the penny- 

 wise pound-foolish policy which unfortunately prevails with many if not most rail- 

 road companies, to the detriment of the public and the stockholders, and the neces- 

 sity fur competent demonstration of the financial superiority of stable, lasting struc- 

 tures on permanent roads. — B. E. F.] 



