DISCUSSION. 159 



The table shows the relative strength of timber columns subjected 

 to direct compression, as would be the case in a column 1 2 inches 

 long and 3 inches by 3 inches in section, compared with a 

 column 6 feet long and 2 inches by 2 inches in section, or with 

 a ratio of length to smallest dimensions of 4 to 1 compared with 

 36 to 1. The short columns failed by direct crushing of the 

 fibres, while the long columns failed by buckling transversely, 

 and the tables give at once the compression per square inch at 

 which failure occurs without any calculation. The behaviour 

 of long and short timber columns have been investigated by 

 Professor Rankine, Gordon and Shaler Smith, but their formulae 

 are mathematically incorrect, although they are approximately 

 correct, for those cases in which the constants y*and a have been 

 determined under similar conditions to those existing in the case 

 under consideration, and from the data contained in the fore- 

 going table it would be an easy matter to calculate the values of 

 the constants f and a for Australian timbers, but the experimental 

 results given in the table render the formula unnecessary for 

 Australian timbers. The most complete investigation of the 

 strength of long columns is that given by Professor R. W. Smith, 



-of the Mason College, Birmingham, published in the Engineer 

 for October, 1887, pages 303, 345, and 425, and I recommend it 

 to all those who are interested in the subject. In conclusion, I 

 am glad that the paper has called forth such a good discussion, 

 and my thanks are due to those gentlemen who have taken 

 part in it. 



The President — I am sure we are all pleased not only at 

 having had the opportunity of hearing Professor Warren's paper 



.read at the last meeting, but of listening to the valuable discussion 

 upon it. It is to be hoped that the question of our Australian 

 timber will come to the front now it has been shown to be so 



-superior to that hitherto used here in the construction of bridges 



.and so forth. 



Correspondence. 



John A. McDonald, m.i.c.e. — I did not intend taking any part 

 in the discussion on this paper, but on reading over the remarks 

 made by the different members, it appears to me that some points 

 might be brought out more clearly. Mr. Hay croft states, in 

 speaking of the Cowra bridge, " the stresses in the several 

 members of which will, I think, on investigation be found 

 incorrect." I may state that the stresses have been thoroughly 

 investigated, as might have been judged by the paper, and Mr. 

 Hay croft's statement that he only "thinks" they will be found 

 incorrect, seems rather to admit a doubt of his own calculations. 



