process of making them. The patentee is not
the only one who can reach a goal,--the production of a certain
article,--but he is the only one who can reach it by a particular
path. A patented machine for welting shoes stops no one from making
shoes, but it forces every one who would make them, except the
patentee or his assigns, to resort to a less economical process.

_Patents Limited in Duration indispensable as Dynamic Agents._--If an
inventor had no such protection, the advantage he could derive would
be practically _nil_, and there would be no incentive whatever for
making ventures except the pleasure of achievement or the honor that
might accrue from it. In the case of poor inventors this would be cold
comfort in view of the time and outlay which most inventions require.
Not only on _a priori_ grounds, but on grounds of actual experience
and universal practice, we may say that patents are an indispensable
part of a dynamic system of industry. It is also important that the
monopoly of method which the patent gives should be of limited
duration. If the method is a good one and the profit from using it is
large, the seventeen years during which in our own country a patent
may run affords, not only an adequate reward for the inventor, but an
incentive to a myriad of other inventors to emulate him and try to
duplicate his success. Ingenious brains, which are everywhere at work,
usually prevent the owners of a particular patent from keeping any
decisive advantage over competitors during the whole period of
seventeen years. Long before the expiration of that time some device
of a different sort may enable a rival to create the same product with
more than equal economy, and the leadership in production then passes
to this rival, to remain with him till a still further device effects
a still larger economy and carries the leadership elsewhere. That
alternation in leadership which we have described and illustrated
takes place largely in consequence of our system of patents; and yet
every particular patent affords a quasi-monopoly to its holder. The
endless succession of them insures a wide diffusion of advantages. At
the expiration of each patent, even if it has not been supplanted by a
later and more valuable one, the public gets the benefit of the full
economy it insures, and wherever an unexpired patent is supplanted by
a new one, the public gets this benefit much earlier. Cost of
production tends rapidly downward, and t