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That may enlarge the use of a thing, but does not make it a new thing. If a part of what is claimed is not new, and that part is severable from the residue which is new, the statute provides for a disclaimer by the patentee of that part of his claim, leaving the patent valid as to so much as was new. The cases have determined many interesting questions concerning the important subject of disclaimer, as our notes will show. (i) A reissue is granted ff to the original patentee, * his heirs, or the assignees of the entire interest, on a surrender of the original patent, when, by reason of an insufficient or defective specification, the original patent is invalid, if the error has not arisen from any fraudulent intention. But only what is so described or shown in the original patent, can be the subject of a reissue.1 The patentee may, however, have a separate patent for each distinct and separable part of the invention comprehended in the original application.

Greenwood, 11 How. 266; Phillips v. Page, 24 How. 164; Bray v. Hartshorn, 1 Clif. 688; Brooks v. Aston, 8 Fl. & Bl. 478; Steiner v. Heald, 6 Exch. 607; Horton v. Mabon, 12 C. B. (n. s.) 437; App. 16 id. 141; Harwood v. G. N. B. R. 11 H. L. C. 664. Nor can a patent be taken for a particular use of a known machine, although the plaintiff be the first to dis-cover the benefit of such use. Tetley v. Easton, 2 C. B. (n. s ) 706; Ralston v. Smith, 11 H. L. C.228.

(i) Statute 1870, § 54. "Whenever through inadvertence, accident, or mistake, and without any fraudulent or deceptive intention, a patentee has claimed more than that of which he was the original or first inventor or discoverer, his patent shall be valid for all that part which is truly and justly his own, provided the same is a material or substantial part of the thing patented; and any such patentee, his heirs or assigns, whether of the whole or any sectional interest therein, may, on payment of the duty required by law, make disclaimer of such parts of the thing patented as he shall not choose to claim or to hold by virtue of the patent or assignment, stating therein the extent of his interest in such patent; said disclaimer shall be in writing, attested by one or more witnesses, and recorded in the Patent-Office; and it shall thereafter be considered as part of the original specification to the extent of the interest possessed by the claimant, and by those claiming under him, after the record thereof. But no such disclaimer shall affect any action pending at the time of its being filed, except so far as may relate to the question of unreasonable neglect or delay in filing it" By section 60 it is further provided, that without entering a disclaimer, the patentee may sue either at law or in equity for the infringement of such parts of his patent as are bona fide his own. But if a disclaimer is not filed before the commencement of the suit, he shall recover no costs; and if he unreasonably neglect or delay to file a disclaimer, he shall not be entitled to the benefits of this section. See Hall v. Wiles, 2 Blatchf. 198; Singer v. Walmsley, 1 Fish. 674; Carhart v. Austin, 2 Fish. 629; M'Cormick v. Seymour, 8 Blatchf. 209, 19 How. 106. But a disclaimer is necessary only where the thing claimed without right is a substantial and material_part of the thing patented. Hall v. Wiles, 2 Blatchf. 198. Unreasonable delay in filing a disclaimer, when one is necessary, is a good defence to an action or suit upon the patent. What delay is reasonable is usually a mixed question of law and fact, to be decided by the jury under the instructions of the court, but is sometimes a question of law for the court alone. Reed v. Cutter, 1 Story, 600; Brooks v. Bicknell, 3 McLean, 449; O'Reilly v. Morse, 16 How. 122; Silsby v. Foote, 20 How. 387; Singer v. Walmsley, 1 Fish. 676; Parker v. Stiles, 6 McLean, 66. A disclaimer affects only the interest of the party who makes it Wyeth v. Stone, 1 Story, 294; Potter v. Holland, 1 Fish. 327; Smith v. Mercer, 1 Pens. L. J. 641.

1 See Manufacturing Co. v. Corbin, 103 U. S. 786, and cases cited.

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It must be "useful." This means that it must not be harmful and opposed to the public welfare. (j) Then, that it promises some positive advantage; (k) and included in this is the implied requirement, that the means employed do actually produce the result attributed to them; for, if they fail, the invention would be of no use, or certainly not useful in the manner the applicant has asserted. (l)

* The words "art, machine, manufacture or compo gg sition of matter" have been repeatedly under consideration by the courts. But the result is only that, as they were intended to embrace almost, if not quite, every possible mode of accomplishing a useful result by physical means, so they have about this extent in law. (m)

It has been recently held in England that the use of a new material to produce a known article is not the subject of a patent. (mm) l

One rule is of great importance and is always regarded; although it is not easy to define it, and is often of very difficult application. It is, that a patent cannot be granted, or is void if granted, for a mere property or function of matter, a motive power of the elements, or a physical law or force. But any of these being discovered, or a new use of any of them, the discoverer or inventor may have a patent for his mode or method of applying it to use.

Hence, it is now settled, that a patent may be taken out for "a process." What the limits are to the application of this rule, it

(j) Lowell v. Lewis, 1 Mast. 186; Kneass v. Schuylkill Bank, 4 Wash. 12; Langdon v. DeGroot, 1 Paine, 204; Whitney v. Emmett, Bald. 309; Dickenson v. Hall, 14 Pick. 220; Roberts v. Ward, 4 McLean, 566; Page v. Ferry, 1 Fish. 298: Poppenhausen v. N. Y. G. P. C. Co. 2 Fish. 62.

(k) Many v. Jagger, 1 Blatchf. 381; Wilbur v. Beecher, 2 id. 137; Bedford v. Hunt, 1 Mass. 808; Dunbar v. Marden, 13 N. H. 319.