wastes time and energy; the housewife who washes with her hands alone
and does not aid herself by the use of washing machine and proper
bleaching agents dissipates energy sadly needed for other duties.

The Chapter on machines is intended not only as a stimulus 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