PEEFACE TO SECOND EDITION. XV11 



all ordinary spans, apart from the method of erection, the sim- 

 ple girder need fear no rivalry. JBut for long spans of large 

 number it is not yet clear how the very large theoretical saving 

 is counterbalanced by the objections hitherto urged, such as 

 varying modulus of elasticity, inapplicability of theory to 

 framed structures, effects of temperature, etc. ; nor is it quite 

 clear exactly how the effect of such objections is estimated. 

 That such objections have weight is not to be denied. That 

 their weight is sufficient to condemn the system is the very 

 point at issue. This point we decline to decide either way, 

 without better reasons than have thus far been advanced. 

 Thus, not pretending to decide it ourselves, we cannot but 

 regard those who do, as hasty. The question now is one 

 for the workshop. So far as theory can go we give it here, 

 in a more perfected and practical shape than ever before 

 given. The mathematicians have done their part, and pre- 

 sented their results. It remains now for the practical engi- 

 neer and constructor to do their part. Only by concert of action 

 can the truth be attained. " If brought to the test of practice, 

 the theory is found at fault and its results delusive well. If 

 not, well also. In either case engineering art and science are 

 advanced." Until, however, the question is thus settled, we 

 must regard it as an open one, and trust it will " periodically 

 turn up for settlement " until thus finally disposed of. Unless 

 the theory of flexure, so long accepted as practically valuable 

 and received by practical engineers, can be replaced by a better, 

 we must especially deprecate all attempts to arbitrarily settle 

 the question by fruitless discussion. We cannot thus sum- 

 marily pronounce upon a theoretical question without theory, 

 and upon a practical question without practice; nor is this 

 the spirit in which progress in knowledge or practice can be 

 made. 



It may be well to remember, in this connection, that other 

 nations have brought or are bringing the question to a practi- 

 cal test. England, France, Germany, Austria, Prussia, Spain, 

 Italy have tried or are trying the case, and have not yet 

 decided it. The skill of American engineers, as exemplified in 

 our present practice, needs no encomium. It is world-wide. 

 They might, indeed, be reasonably expected to succeed even 

 where others fail, and if there be any advantage in the system, 

 they, if any, might be expected to find it. 



