mulus 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 understand 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 instruments. 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 nothing 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 the average adult mind as
well, is singularly non-logical and incapable of continued
concentration, and loses interest under too consecutive thought and
sustained style. For this reason the author has sacrificed at times
detail to general effect, logical development to present-day interest
and facts, and has made use of a popular, light style of writing as
well as of the more formal and logical style common to books of
science.

No claim is made to originality in subject matter. The actual facts,
theories, and principles used are such as have been presented in
previous textbooks of science, but the manner and sequence of
presentation are new and, so far as I know, untried elsewhere. These
are such as in my experience have aroused the greatest interest and
initiative, and such as have at the same time given the maximum
benefit from the informational standpoint. In no case, however, is
mental training sacr