Mr. Justice Bradley,

after stating the case as reported above, delivered the opinion of the court.

The questions to be decided, therefore, are whether the English patent (which was given in evidence) was for the same invention as the American patent; and, if so, whether the latter is limited to expire at the end of seventeen years *283 from the sealing of the former. "We think that both of these questions must be answered in the affirmative.

As to the first question, we have carefully compared the two patents, the English and American, and can see no essential difference between them. They describe the same furnace in all essential particulars. The English specification is more detailed, and the drawings are more minute and full; but the same thing is described in both. There is only one claim in the English patent, it is true. But that claim, under the English patent system, entitled the patentees to their entire invention, and is at least as broad and comprehensive as all four claims in the American patent. It is in these terms:

“ Having now described the nature of our invention and the best modes wrn are acquainted with of performing the same, we wish it to be understood that we do not confine ourselves to the precise details shown on the accompanying drawings; but we claim as our invention the various arrangements of regenerative furnaces worked by the gases resulting from an imperfect combustion of solid fuel in separate places, as hereinbefore set forth.”

It is contended by the counsel of the complainants, that the American patent contains improvements which are not exhibited in the English patent. But if this were so, it would not help the complainants. The principal invention is in both; and if the American patent contains additional improvements, this fact cannot save the patent from the operation of the law which is invoked, if it is subject to that law at all. A patent cannot be exempted from the operation of the law by adding some new improvements to the invention; and cannot be construed as running partly from one date and partly from another. This would be productive of endless confusion.

We have, then, to examine the question whether the term of the American patent was limited to run from its own date, or from the date (or sealing — which is equivalent to the publication) of the English patent. The reissued patent sued on is dated January 12, 1869, but the original patent, which is *284 the one to be looked at, was dated March 1, 1864. It was issued, therefore, before the act of July 8, 1870, 16 Stat. 198, c. 230, by which the patent laws were revised, and whilst the acts of July 4, 1836, 5 Stat. 117; March 3,1839, 3 Stat. 353; and March 2, 1861, 12 Stat. 246, were in force. The act of 1S36, as well as previous acts, made the term of a patent fourteen years; but it authorized an extension of the term for seven years longer, if it should appear that the patentee, without neglect or fault on his part, failed to obtain a reasonable remuneration for his invention. By the same act (§ 7) if an invention for which a patent was sought had been patented in a foreign country, before the application for a patent here, it was a bar to obtaining a patent in this country, unless (§ S) such foreign letters-patent had been taken out by the applicant himself within six months previous to the filing of his specification and drawings. The act of 1S39, § 6, removed the limitation of six months, and allowed a patent to be taken out here at any time after the inventor had taken out a jiatent for the same invention in a foreign country, provided it should not have been introduced into public and common use in the United States prior to the application for a patent here: “ And provided also, that in all cases every such patent shall be limited to the term of fourteen years from the date or publication of such foreign letters-patent.”

The act of 1861 introduced several changes in the administration of the Patent Office, and gave a right to patents for designs. The last section (§ 16) declared as follows, to wit, “ that all patents hereafter granted shall remain in force for the term of seventeen years from the date of issue; and all extension of such patents is hereby prohibited.”

The act of 1870, which was a revision of all previous laws relating to patents, continued the period of seventeen years as the term of a patent, and in case a foreign patent had been previously issued, declared that the American patent should expire at the same time with the foreign patent, or, if more than one, at the same time with the one having the shortest term; but, in no case, for a longer term than seventeen years. This provision is substantially carried forward into the Revised Statutes, § 4887.

*285 The appellants contend that the act of 1861 repealed that portion of the act of 1839 which declared that a patent should be limited to the term of fourteen years from the date or publication of prior foreign letters-patent for the same invention. So far as the period of fourteen years is concerned, this is, undoubtedly, true. Prior to 1861 all patents, as we have seen, were granted for the term of fourteen years, with a right, under certain circumstances, to an extension for seven years longer. This right of extension was attended with many inconveniences and much expense to meritorious patentees, and Congress, by the act of 1861, cut it off, and made the term of all patents seventeen years — a compromise between fourteen and twenty-one years. The act had nothing to do with the question of foreign patents, but only with the term for which patents should ordinarily run; and the period of seventeen years, without any privilege of extension, was adopted in lieu of fourteen years with a provisional right of extension. That was the sole point before the legislative mind. Seventeen years limit was substituted for fourteen years. That was all that was intended or thought of. We are of opinion, therefore, that the condition imposed by the act of 1839, that the term of a patent for an invention which has been patented in a foreign country, shall commence to run from the time of publication of the foreign patent, was not repealed or abrogated by the act of 1861. If it was, it follows that there was a period of nine years, from 1861 to 1870, in which our patent system presented the anomaly of allowing patents to be taken out in this country at any length of time after the invention had been patented abroad, and without being subject to any condition, limitation, or restriction. This can hardly be supposed to have been the intention of Congress.

No doubt, the words of a law are generally to have a controlling effect upon its construction; but the interpretation of those words is often to be sought from the surrounding circumstances and preceding history. From the history of the law in this case, as exhibited in previous enactments, and from the evident object and purpose of § 16 of the act of 1861, *286 we are satisfied that the words there used to define and limit the term during which patents thereafter granted should remain in force, namely, "seventeen years from the date of issue," were only intended to change the length of the term, and not the point of its commencement. The latter continued as before, at "the date of issue," as defined by previous laws — referring either to the issue of the American patent itself, when no foreign patent had been previously obtained, or to that of the latter when such a patent had been obtained. This view of the construction and meaning of the act of 1861 was fully explained and enforced by Mr. Justice Blatchford in the case of De Florez v. Raynolds, 17 Blatchford, 436; S.C. 8 Fed. Rep. 434.

The decree of the Circuit Court is affirmed.