INTRODUCTORY. 7 



plates, when its behaviour under a tensile test becomes 

 important ; if for the rivets of the same boiler, its shearing 

 strength should be known ; it may be used in the manu- 

 facture of pillars or struts, when its compressive strength 

 is required to be known ; or, it may be that the steel is 

 required to construct a propeller shaft of, when its properties 

 under a test in torsion are necessary. 



And so it is all through. As a rule, it is not sufficient 

 to know the general strength properties of a substance, 

 but the properties which exhibit themselves under special 

 circumstances and when made of special forms, must also 

 be known, and the tests applied should always be 

 judiciously selected and carried out, so that the actual 

 conditions of use may be as nearly as possible satisfied. 



In making a study of the subject of testing, it is 

 necessary that the reader should in the first place have 

 some knowledge of that part of the science of mechanics 

 which deals with stresses and strains of various kinds, as 

 such a knowledge is absolutely necessary in reducing the 

 results of many of the tests and experiments he will have 

 to perform. It has, therefore, been assumed by the author 

 that the reader of this book does not approach the subject 

 as an absolute novice to the subject. At the same time a 

 chapter will be devoted to what is little more than a 

 summary of the principal problems Avhich have to be 

 attacked when dealing with the phenomena displayed by 

 bodies under various stresses. In this will be explained 

 briefly the chief of the principles involved, and such 

 formulas as are required will be given. It is, however, 

 of the utmost importance that a mere carrying out of 

 experiments, and calculating the results from the formula) 

 given, will be of very little service to the student. He 

 should have nothing to do with an experiment unless he 

 is perfectly clear in his own mind as to all the principles 

 involved. 



It will be seen that following on the chapter which has 

 just been mentioned, the various testing appliances are 

 described, the methods employed in carrying out all the 

 principal branches of testing, and the behaviour of the 

 different materials of engineering under stresses of various 

 kinds, is considered so far as is possible within the narrow 

 limits of such a work as this. 



It seems hardly necessary to repeat what has already 

 been said, namely, that in all testing work, neatness, order 

 and systematic working and booking should be strenuously 



