PREFACE 



This book and its companion volume for the wood-working 

 trades, first cover the general principles of science common to 

 all industry, this material Being identical in the two books. 

 Additional material follows this, that relating specifically 

 to the metal trades appearing in this volume, and that re- 

 lating particularly to the wood-working trades appearing in 

 " Applied Science for Wood- Workers." The books are con- 

 structed in this way to meet the needs of particular indus- 

 trial, trade, continuation, or apprentice classes where the 

 instruction is intensive. 



Every craftsman should not only be trained in the handi- 

 craft of his trade, but, if he is to be a really skilled worker, 

 should also master the scientific principles involved; that is, 

 he should become familiar with the reasons underlying the 

 various operations which he performs. Such knowledge is 

 obtained through the study of industrial science. The teach- 

 ing of related trade knowledge is not, so far as the author 

 knows, adequately covered in any system of industrial 

 education. 



Experience proves that, though the average pupil who 

 completes the regular high school course may know the prin- 

 ciples of the sciences in an abstract way, he is unable to 

 recognize these principles in operation in the every-day work 

 of the world. This fact is not surprising. Observation shows 

 that many minds are able to grasp a principle in the abstract 

 but are not able readily to apply that principle in practice. 



