ough evidence to
defeat a patent. Much less evidence, however, might be sufficient to
prove that a very simple invention had been anticipated.

To justify the granting of a patent it must be useful. If the
invention be frivolous or pernicious, the inventor cannot secure for
it legal protection. The use of the invention must not be contrary to
public health or morals. It is not needful that the invention should
be the best of its kind, or that it should accomplish all that the
inventor claims for it. Furthermore, its utility depends on the state
of the art at the time of making the claim or issuing the patent; its
subsequent inutility does not invalidate the patent. Extensive use is
evidence of utility. The presumption of law favors a patent, and the
burden of proof is on the one attacking it to show that it is not
useful. The infringement of an invention is in effect an admission of
utility, because use implies utility.

A patent also calls for the exercise of inventive power. Though
invention must be seen in every patent, it is difficult to define.
Says a former commissioner of patents, Justice Duell: "It is a matter
resting in judgment and therefore no fixed rule for its determination
is possible." Some principles, however, assist in defining the term.
"Thus, it is declared that an act of invention is primarily mental and
involves the conception or mental construction of a means not
previously known for accomplishing a useful result. It is not the mere
adaptation of old means by common reasoning, but is the construction
of new means through an exercise of the creative faculties of the
mind." Between invention and discovery the patent laws draw no
distinction. Again, it has been often said that the design of the
patent laws is to reward those who make a substantial invention or
discovery, which is an additional step in the useful arts. The law
never intended to grant a monopoly for every trifling device which
would naturally occur to a skilled mechanic in the ordinary progress
of manufacture.

An article of manufacture is not patentable because means have been
devised to make it more perfectly than before; it must be new in
itself and not merely in its workmanship. A machine-made article
therefore is not patentable simply because it is thus made, and no
longer by hand.

The substitution of an art, manufacture, or composition of matter of
one element or device for another which does the same thing in the
same way