EDITORIAL NOTE 



THE DIRECTLY-USEFUL TECHNICAL SERIES requires a few 

 words by way of introduction. Technical books of the past 

 have arranged themselves largely under two sections : the 

 Theoretical and the Practical. Theoretical books have been 

 written more for the training of college students than for the 

 supply of information to men in practice, and have been greatly 

 filled with descriptions of an academic character. Practical 

 books have often sought the other extreme, omitting the scientific 

 basis upon which all good practice is built, whether discernible 

 or not. The present series is intended to occupy a midway 

 position. The information, the investigations, and the problems 

 are to be of a directly-useful character, but must at the same 

 time be wedded to that proper amount of scientific explanation 

 which alone will satisfy the inquiring mind. We shall thus 

 appeal to all technical people throughout the land, either students 

 or those in actual practice. 



