544 FECERAIi BEPOKTKB. �that Estabrook and his partner are the persons wtomake the nails used by the defendants; and the defendants admit that one of the nails which they use infringes both patents ; but they deny that the other, or "cub" nail, infringes; and deny that either patent is valid. �There is no conflict of evidence in respect to the principal patent, 90,902. It is admitted by the defendants that the nail is specifically new, and by the plaintififs that the "Bent" nail, •which was patented more than a year before June, 1869, is substantially like Whidden's nail, except that the latter bas corrugations on the sides, which undoubtedly serve a useful purpose in holding the nail in place. The question is ■whether the addition of corrugations to the "Bent" nail is a patentable improvement, in view of the fact, admitted in the specification, that shoe nails hadbeen corrugated before June, 1869. �This question of patentability is often one of very great embarrassment. The patent law requires the presence of what it calls invention, as contradistinguished from con- structive ability; but it furnishes no test, for ail cases, by which they can be diacriminated. The decision does not necessarily depend upon the amount of thought, or even of experiment, which may have been had in reaching the resuit. Thus, if an old machine or process is put to a new use, in- vention is positively excluded, although the new use mayappar- ently be very remote from the old, requiring experiment to ascertain its practicability; and though the actual operation of the machine or process may not be exactly the same in the new as in the old application, provided no new means are, in fact, employed. �When the patentee has produced something new, the ques- tion is more difficult. Some changes, such as a substitution of brass for iron, or of steam-power for horse-power, are, at the present day, presumed to be within the common knowl- edge of mechanics. �Does the addition of corrugation to a emooth shoe nail come within this class of cases? It is impossible to give a wholly satisfactory reason for answerjng this question either ����
