582 THE POPULAR SCIENCE MONTHLY. 



sciousness as acting simultaneously. And similarly, to understand 

 social progress in the vast sweep of its course, there must he ever 

 present to the mind the egoistic and the altruistic forces as coopera- 

 tive factors equally indispensable, and neither of them to he ignored 

 or reprobated. 



The criticism likely to be passed on this chapter, that "The 

 Educational Bias" is far too comprehensive a title for it, is quite 

 justifiable. There are in truth few, if any, of the several kinds of 

 Mas that are not largely, or in some measure, caused by education 

 usino- this word in an extended sense. As, however, all of them could 

 not be dealt with in one chapter, it seemed best to select these two 

 opposite forms of bias which are so directly traceable to teachings of 

 opposite dogmas, and fosterings of opposite sentiments, during early 

 life. Merely recognizing the fact that education has much to do with 

 the other kinds of bias, we may now most conveniently deal with 

 these, each under its specific title. 



THE STRENGTH OF TIMBER. 1 



By JOHN ANDERSON, C. E., LL. D., F. E. B. E. 



ALTHOUGH it is of less importance to investigate the strength 

 of timber at the present time than it was formerly, in conse- 

 quence of the diminished use of that material in permanent structures, 

 and the more general employment of iron, still it will always be a 

 very valuable material for certain purposes, and ought not to be neg- 

 lected. Timber is variously used, even now, in permanent works, and 

 is applied much more extensively in temporary structures such as 

 centerings and scaffolding. Hence its properties are well worthy of 

 careful attention ; and the student should be familiar, not only with 

 the external appearance of the principal kinds of wood, but also with 

 their relative strength, stiffness, toughness, and durability. 



One of the most obvious inferences to be drawn from the experi- 

 ments previously recorded is, that very wide variations exist in the 

 strength and other elastic properties of different metals, and even of 

 different specimens of the same metal. If we could investigate the 

 properties of timber with the same care which has been bestowed on 

 the metals, we should find that there is an even greater variation in 

 the properties of different kinds of wood. This arises, in part, from 

 the fact that timber is much affected by a number of external and in- 

 ternal conditions, during its growth and seasoning, and in its subse- 

 quent treatment, which gradually modify and change its properties. 

 1 From " Strength of Materials and Structures." D. Appleton & Co. 



