(l) Manton v. Parker, Dav. Pat Cas. 827; Roberts v. Ward, 4 McLean, 565; Curtis on Patents, § 248; O'Reilly v. Morse, 16 How. 119. The superior utility of a machine, though not of itself ground for a patent, is often evidence of the introduction of some new principle or mode of operation. Many v. Sizer, 1 Fish. 17; Judson v. Cope, id. 615; Johnson v. Root, id. 851; 2 Clif. 108. If the defendant has used the patented improvement, he is estopped from denying its utility. Vance v. Campbell, 1 Fish. 483; Hays p. Sulzor, id. 532.

(m) A construction equally broad has been given by the English courts to the word "manufacture" in the Statute of Monopolies, on which the patent law of England rests. See Crane v. Price, 4 McN. & G. 680; Hill v. Thompson, 3 Meriv. 626; Boulton v. Bull, 2 H. Bl. 463.

(mm) Rushton v. Crawley, L. R. 10 Eq. 522.

1 Thus the substitution of a known equivalent for one of the elements of a former structure, as a rigid for a flexible leather cross-bar on shawl-straps, is not patentable Crouch v. Roomer, 103 U. S. 797.

hh would be difficult to determine in the present state of the hh authorities, which we exhibit in our notes. (n)1 * This

(n) The leading English case upon this point is Neilson v. Harford, 1 Webst. Pat Cas. 278. Prior to the plaintiff's invention, furnaces for the manufacture of iron had been worked by a blast of cold air. He discovered that, by using hot air instead of cold, a great improvement in the quality of the iron would be effected. In his specification he merely directed heating the air on its passage from the blowing apparatus to the furnace, by passing it through a vessel artificially heated; but gave no direction as to temperature, and even declared that the form or shape of the vessel was immaterial to the effect, and might be adapted to the local circumstances or situation. On the trial it was strenuously urged that the claim was for the general principle of using hot air in the blast, independent of any mode of making the application, and therefore void as an attempt to patent a principle. It was held otherwise. Baron Parke, delivering the opinion of the court, said: "It is very difficult to distinguish this specification from that of a patent for a principle; but after full consideration, we think that the plaintiff does not merely claim a principle, but a machine embodying a principle, and a very valuable one. We think the case must be considered as if, the principle being well known, the plaintiff had first invented a mode of applying it by a mechanical apparatus to furnaces; and his invention then consists in this, - by interposing a receptacle for heated air between the blowing apparatus and the furnace. In this receptacle he directs the air to be heated by the application of heat externally to the receptacle, and thus he accomplishes the object of applying the blast, which was before of cold air, in a heated state to the furnace." And in another suit upon the same patent, House-hill Co. v. Neilson, 1 Webst. Pat. Cas. 683, Lord Justice Clerk Hope, in his charge to the jury, said: "It is quite true that a patent cannot be taken out solely for an abstract philosophical principle, - for instance, for any law of nature, or any property of matter, apart from any mode of turning it to account in the practical operations of manufacture, or the business, and arts, and utilities of life. The mere discovery of such a principle is not an invention, in the patent-law sense of the term. But a patent will be good, though the subject of the patent consists in the discovery of a great, general, and most comprehensive principle in science or law of nature, if that principle is by the specification applied to any special purpose, so as thereby to effectuate a practical result and benefit not previously attained." And again he says: "I state to you the law to be, that you may obtain a patent for a mode of carrying a principle into effect; and if you suggest and discover, not only the principle, but suggest and invent how it may be applied to a practical result by mechanical contrivance and apparatus, and show that you are aware that no particular sort, or modification, or form of the apparatus, is essential, in order to obtain benefit from the principle, then you may take your patent for the mode of carrying it into effect, and are not under the necessity of confining yourself to one form of apparatus." This ruling was afterwards sustained by the House of Lords, though the case was reversed upon another point To the same effect are the observations of Baron Alderson in Jupe v. Pratt, 1 Webst. Pat. Cas. 146: "You cannot take out a patent for a principle; you may take out a patent for a principle, coupled with the mode of carrying the principle into effect, provided you have not only discovered the principle, but invented some mode of carrying it into effect. But then you must start with some mode of carrying it into effect; if you have done that, then you are entitled to protect yourself from all other modes of carrying the same principle into effect, that being treated by the jury as piracy of your original invention." And this is at this day the law of England on this point See Bovill v. Key worth, 7 EL & Bl. 724; Booth v. Kennard, 1 Hurl & N. 527; Seed v. Higgins. 8 El. & Bl. 771, 8 H. L. C. 550; Curtis on Patents, § 141. In this country the inventor would seem to be confined within much narrower limits. Thus, in O'Reilly v. Morse, 16 How. 62, it was conceded by the court that the defendant in error was the first to apply electro-magnetism to practical use for telegraphic purposes, and that he was justly entitled to a patent for the particular process he had discovered; but his claim was declared void as being for a principle. The claim

1 See Tilghman v. Proctor, 102 U. S. 707, for a discussion of this question, and comments on O'Reilly v. Morse, ante.

ii process is the method of reaching a certain result. It differs from a "machine;" for a patent for a machine covers