4 PREFACE 



The Chapter on machines is intended not only as a stimu- 

 lus to the invention of further labor-saving devices, but also 

 as an eye opener to those who, in the future struggle for 

 existence, must perforce go to the wall unless they under- 

 stand how to make use of contrivances whereby man's limited 

 physical strength is made effective for larger tasks. 



The Chapter on musical instruments is more detailed than 

 seems warranted at first sight ; but interest in orchestral 

 instruments is real and general, and there is a persistent 

 desire for intelligent information relative to musical instru- 

 ments. The child of the laborer as well as the child of the 

 merchant finds it possible to attend some of the weekly 

 orchestral concerts, with their tiers of cheap seats, and noth- 

 ing adds more to the enjoyment and instruction of such hours 

 than an 'intimate acquaintance with the leading instruments. 

 Unless this is given in the public schools, a large percentage 

 of mankind is deprived of it, and it is for this reason that 

 so large a share of the treatment of sound has been devoted 

 to musical instruments. 



The treatment of electricity is more theoretical than that 

 used in preceding Chapters, but the subject does not lend 

 itself readily to popular presentation ; and, moreover, it is 

 assumed that the information and training acquired in the 

 previous work will give the pupil power to understand the 

 more advanced thought and method. 



The real value of a book depends not so much upon the 

 information given as upon the permanent interest stimulated 

 and the initiative aroused, The youthful mind, and indeed 



