is to be used, and, after all this, the greatest
obstacle of this kind is to be met in the man who uses the
machine. For it is in his hands that a machine must prove its
value.

When we consider the inertia of mind and body, it is truly
marvelous that there has been any progress in machine design. In
fact, if the machine-building trade were in retrogression, with
only a few new men being taken in there would be little or no
excuse for making machine tools of new design. The older workers
would get along about as well without the improved machines.

This is not said in a spirit of fault finding. It is a great fact
that we should grasp if we are to design machinery successfully.

It is difficult for the man of sanguine temperament to really
accept this view, and it is also hard for one who is continually
searching for knowledge. But it must be appreciated, and all work
must conform to this principle, if it is to be pushed forward
along the lines of easiest progress.

Accepting this view is no barrier to progress. It will not
ultimately delay the work of a reformer if he is induced to act in
accordance with this principle. It only prevents a wreck.

The knowledge of the force of habit of man should therefore be
used in two ways:

First, when the designer is trying to make the most natural
machine for the purpose. Then he must overcome his own tendency to
follow precedent. Second, when considering the kind of a machine
that can be easily made, sold, and used, he must give due
consideration to the inertia of others, for their inertia he
cannot hope to quickly change. Reformers in this world generally
have a hard time whenever they under estimate the inertia of men's
minds and bodies.

A designer of machinery, by close application to his tasks, should
obtain a clearer view than it is possible for others to possess,
of the way a machine should be designed, made, and used. It is not
necessary to assume he has a better brain. An ordinary mind
applied to a given subject sees it more clearly than an abler mind
which has not considered the subject with the right interest.

Inventions Should Not Mix With Details.

In first working out the mechanical schemes no energy should be
wasted in trying to make the sketches correct in proportion. The
very functioning of the brain along the draftsman's line shifts it
away from the inventive mood. The exact drawing frequently shows
the necessity of change in general scheme, bu