carrier, works under and obeys some law peculiar to 

 itself. Unless both manufacturer and operator under- 

 stand the various laws and principles which govern a 

 device, it is liable to fail to perform the functions 

 intended, though both parties may have had unlimited 

 experience. This necessary understanding or knowl- 

 edge can be gained much more easily and successfully 

 than by depending upon the slow process of the 

 school of experience to educate and teach what 

 should have been understood at the beginning. As 

 the mind will grasp information from any source 

 within reach, the written rule is much the better 

 method by which to gain a knowledge of the laws 

 and principles. The mind must first be informed and 

 then the hands made skillful. Recognizing this, the 

 author has endeavored to place before the reader 

 such an exposition of the subject under consideration 

 as will best enable him to reap the best results from 

 his labor. 



If this book is the means of aiding anyone in his 

 part of the work, the author will feel conscious of 

 being well repaid for the labor and time consumed 

 in preparing it. 



Due acknowledgement is hereby extended to all 

 who have aided in any way to make it a success. 



GEORGE F. CONNER. 



