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 Ch.X. Sec.IL] Patents. 191 actly identified. Another reason for general expressions is, to guard against the opposite party obtaining a knowledge of the invention, as he might be able to affect the validity of the patent, by publishing the invention before the patent is sealed, which would have the effect of throwing the invention open to the public. But it will sometimes happen, that two ingenious persons may, without any improper communication, make a discovery of a similar invention, in which case, upon the simi- larity of the invention appearing to the attorney or solicitor- general, it is usually recommended that the parties should unite interests, and take out a patent in their joint names, which seems to be the most prudent plan for both parties, as priority of invention would be of no avail, if the other party should be inclined to publish the invention, so as to affect the patent. We cannot, however, too much reprobate a practice, which has of late grown into use by some speculative persons, of keeping a list of caveats upon general principles entered in the books, without any idea of obtaining patents themselves, but with the sole view of being acquainted with every improve- ment that is going on, whereby they gain an opportunity of coming to a compromise with the real inventors, and sometimes have obtained large sums of money from them, to withdraw their opposition." It will have been collected from the cases cited before {a that great care must be observed in stating for what the patent is taken out, and that an error in this respect may be fatal. By provisoes in the patent, the grant becomes void if the patent right become vested in five different persons at the same time, or if the specification be not enrolled within the time. The term for which the patent is granted can only be pro-- longed by Act of Parliament. Fifthly^ Of the remedies for the infraction of the patent right. The exclusive right of the patentee " to work and jnake" the subject-matter of the grant, is infringed by any other per- son copying any part of the invention. And though the ma- chine, &c. made by the defendant be inform difierent from the (a) Ante, 184, 168. patentee's,