

INTRODUCTORY. 5 



it may be determined whether the tests do satisfy the 

 requirements, and then to apply such and only such tests 

 as may be needful for the purpose. 



In scientific testing the case is different. The observa- 

 tions in a test are generally greater in number, more 

 accurately made with apparatus of greater precision, 

 enabling the observer to see more deeply, as it were, 

 into the phenomena exhibited during the tests. 



All testing requires a considerable amount of skill, 

 experience, and sound judgment in its execution, and to 

 these should be added some knowledge of mechanics, so 

 far as the " strength of materials " is concerned. System 

 and order should be rigidly adhered to, both in the carrying 

 out of tests and in the manipulation and presentation of 

 the results. Every detail should be most carefully watched 

 and attended to, as one mistake may render useless a test 

 or even a whole series of tests. Nothing is of more 

 importance than a correct idea of perspective so far as 

 accuracy is concerned, and a clear knowledge of the 

 necessary limits of accuracy to be aimed at, and which are 

 possible in the various kinds of work undertaken, should 

 be most carefully cultivated. Useless attempts at extreme 

 accuracy, where extreme accuracy is neither necessary nor 

 possible of attainment, are always absurd, and in some cases 

 actually mischievous. 



The variety of material which is tested, or capable of 

 being tested, is very great. 



At the present day most engineering structures, whose 

 design is governed by considerations of strength, are con- 

 structed of either iron or steel. These metals have 

 asserted their pre-eminence in such work by reason of their 

 combining the advantages of cheapness, strength, and 

 durability to an extent not found to exist in the case of 

 any other material. The kinds of structures built of iron 

 and steel are very numerous. In addition to the bulk of 

 machinery used for purposes of manufacture, the engines 

 which give the motive power to this machinery, and the 

 shafting and gearing which serve to transmit the power 

 from the engines to the machinery; in addition to their use 

 in formation of structures such as these, iron and steel are 

 greatly used for what, in one sense, are more important 

 works. By these are meant structures whose collapse or 

 failure would endanger human life. Of course, this possi- 

 bility exists in the case of most machinery of any size, 

 but it is especially evident in such structures as bridges, 



