after the foregoing statement, delivered the opinion of the court.

Each of the devices in suit is of the well-known general class of temporary binders for books or files of loose leaves, whereby the leaves are, “in effect, permanently bound, but any leaf can be removed, reinserted, or replaced at any desired point.” This fundamental feature is old in the art, and so are the general means employed, of back pieces with associated posts which enter through or engage with the leaves in various ways to hold them in place, while permitting their removal or replacement as occasion requires. The addition of a locking mechanism to provide against unauthorized interferences is not only an obvious expedient, but is shown as well in prior devices. Aside from the peculiar construction of the telescoping posts, which *253serve both (1) to connect the back pieces and permit their movement •'towards and from each other," while preventing complete separation, and (2) to preserve constant co-operation and engagement with the notched leaves, no element of the appellant’s combination is new in itself, nor presents a new use of any old element. Thus back pieces, connecting and co-operating posts, both plain and telescopic, and leaves with perforations, notches, or broken outline, to make them ‘‘removably secured” in the binder, are each shown in like use in analogous devices; and the locking mechanism in this patent is not only a familiar structure, but is identical with one previously employed by Leslie for like purpose, and in public use for more than two years prior to the present application. It is manifest that Leslie was not a pioneer in the art of so-called “loose-leaved binders”; that his advance in the art, through the structure and two-fold service of the posts described in the patent, is completely embodied in the first seven claims, of which no infringement is here alleged; and that the further claims in question, assuming their validity, can receive no broad construction, and surely no construction which would exclude use of the like structure as found in the same art. Indeed, the narrowness of the contention on the paid: of the appellant is thus assumed and stated by counsel in their brief:

“We are not contending for a broad construction that would cover, or be .anticipaled by, any structure that merely shows a pair of back pieces connected by rigid posts, which are expansible, but not entirely separable, and which posts co-operate with notches in the leaves, merely to determine the position and location of the leaves, and not to prevent their removal, because such a construction is admittedly shown in the Waide patent, No. 484,3-19. "What we are contending for has been sot out previously, and is for a pair of back pieces connected by posts, so as to be capable of freely sliding back and forth (as distinguished from being screwed slowly back and forth), and which an> so located and so co-operate with notches in the edges of the leaves as to hold the leaves in position, not merely determining their location, whether the back pieces are expanded or contracted. In other words, we are contending for a construction in which back pieces with telescoping and nonsep-arable posts are employed, co-operating with leaves, so that the leaves are securely held in position, not by any clamping action of the posts, but by reason of the engagement of the posts with the notches in the leaves.”

The invention of the patentee, as recited in the specifications, “re-íales to that class of temporary binders known in the trade as ‘perpetual ledgers,’ and is designed to embody certain improvements whereby they may be made more compact and easily manipulated”; and “it is further designed to fasten the sheets thereof in the binder in such way that any sheet may be extracted from the binder without loosening the remaining sheets from the binder, and thereby possibly disarranging them.” For the purpose indicated, Leslie devised a uew form of two-part post to connect the back pieces, so arranged as to have a limited sliding movement one part upon the other, “whereby the binder may be expanded, but not separated”; and the posts are shaped “to co-operqte with the notches or projections on the edges of the sheets,” being triangular as shown in the patent, “so that any sheet may be extracted without freeing the others from the binder.” In the ordinary form of telescoping the two sections of the post, the one of least diameter would not closely engage the notch in the leaf: *254and, as suck leaves would be liable to displacement, Leslie obviated the difficulty through the shape of his posts, whereby he made a sliding provision in the sections and preserved the post “in holding contact with the broken outline portions [of the sheet] in all positions.” The provision thus made is clearly claimed and fully set forth in the first seven claims of the patent, of which infringement by the appellee is not alleged. The advantage in the improvement for which the appellant contends, if fully conceded, is wholly attributable to this form of post co-operating with the old elements. Substituting the new form for the post shown in various elder devices, and combining it with the old elements found in one and the other, the new combination furnished an improved binder. In the language of the specifications, it was “made more compact and easily manipulated”; and it certainly operated more readily and effectively than the two-part telescoping posts and screw device shown in Waide's patent, No. 484,349, which, is, perhaps, the closest prototype of the Leslie form of post. This means, however, is not entitled to consideration as a. pioneer invention in the sense of the patent law. It was a mere advance in a line marked out by numerous inventions, — a useful step, whereby the binder was manipulated with more convenience and speed, and with less liability to displace the leaves, and the desired removal or replacement of leaves was readily accomplished; obtaining a better result than by the old devices, but hot essentially new. Thus the feature of removability and' reinsertion of the leaves is expressly shown in several of the prior patents, and in the devices of Leslie in use for more than two years before his application for a patent; and the testimony of the inventor, Leslie, on behalf of the appellant, that he knew of no prior binder with such feature, and that he considered his “invention broad enough to cover any binder having this characteristic,” is evidently founded on a misunderstanding. Applying the excellent definition stated by Mr. Justice Bradley in Railway Co. v. Sayles, 97 U. S. 554, 556, 24 L. Ed. 1054, it was not the case of an inventor who “precedes all the rest, and strikes out something which includes and underlies all that they produce,” and thereby “acquires a monopoly and subjects them to tribute’’; but it is an instance of the gradual advance which “proceeds step by step, so that no one can claim the complete whole, and each is entitled only to the specific form of device which he produces, and every other inventor is entitled to his own specific form, so long as it differs from those of his competitors, and does not include theirs.” See, also, Duff v. Pump Co., 107 U. S. 636, 639, 2 Sup. Ct. 487, 27 L. Ed. 517; Boyd v. Hay-Tool Co., 158 U. S. 260, 267, 15 Sup. Ct. 837, 39 L. Ed. 973.

The new combination of the Leslie invention is distinctly set out, with the various elements embodied, within the first seven claims of the patent; the new form of co-operating post being the marked feature according to the fact. The subsequent claims, 8 to 13, inclusive, on which this action is founded, are general in terms concerning the back pieces and co-operating posts, without limitation as to form, They differ in the description of the sheets, mentioned in some of the claims in mere general terms, and in others as notched or “having a broken outline,” and three of the claims contain general *255mention of a looking mt clmnism, while this feature ⅛ omitted in the others. Each claim refers to the effect produced of permitting the withdrawal of any sheet without freeing the others from the post ox* binder; but the means of co-operation for that purpose, consisting of a notch or “broken outline'’ on the side edges of the sheet, is likewise shown in prior patents, — notably in Paxson’s No. 283,053 (1883) and in the British and German patents of -Strauss (1892). These general claims, as a whole, are" aptly described by Mr. Wiles, the expert ex am in cd on behalf of the appellant, in his description of claim 13:

“In this claim, as well as in each of the five preceding claims, the elements are mentioned in general terms, the form of. the parts and the construction of the locking mechanism not being referred to as a limitation, and the form of the sheets being only limited by the descriptive statement that they are formed with broken outlines adapted to co-operate with the posts, in order that the posts may hold the sheets in place.”

The contention on the part of the appellant for a construction of these claims is thereupon stated by the witness, in reference to claim 8, as follows:

“The terms of the claim are such as to include any combination comprising the back pieces, the telescoping posls, and the locking mechanism, provided the parts of the posts are held permanently In their co-operating- relation, no-matter what the form of the i>osts or the construction of the locking mechanism may be.”

And subsequently occurs the further statement that the particular locking" mechanism is not: an essential featux*e, and “any mechanism which serves to hold the back pieces rigidly in their adjusted positions” would be considered a locking mechanism, “so long as it allows the binder to expand without becoming separated.”

Of this contention it is sufficient to remark that the claims so broadened in their scope would conflict with numerous devices shown in the prior art, as indicated above; and while infringements of the terms by the appellee would thus appeal-, the claims would not sustain an action, being too broad, and hence invalid. On the other hand, with the claims construed in conformity with the specifications, and thus-limited, as the authorities require, to the specific device set forth, the actual invention can be protected without interference with the structures which are open to all; and in such view it remains only to ascertain whether the appellee so infringes.

In common with the Leslie [latent, and with its predecessors as well, the Hoffmann combination has the four elements of (1) back pieces, [2) connecting telescopic posts, co-operating with (3) a cut in the side edges of the sheets, and (4) a locking mechanism.

1. The back pieces are unquestioned, as of the common type.

2. The posts are represented by so-called “vertical casings.” chambered one within the other, open on one side, and connected, respectively, with the back pieces at either end, so that they slide telescopically, to permit expansion and contraction of the binder; and these casings are adapted both to protect and engage “the rear edges or projections on the rear part of the leaves.” They differ from the Leslie post in (heir simplicity, and in the absence of any means to prevent separation of the back pieces, which is made distinctive in the Leslie post. Aside from this departure in the function of the post, *256the difference in the form and mode of operation is more marked than that between Leslie’s structure and those of the prior art; for instance, as shown in the Waide telescopic post (No. 484,349), or that of Morehouse (No. 464,731), in the Strauss British patent, and in the Leslie exhibit prior device.

3. The “broken outline” in the edge of the sheet in the appellee’s device differs from that of Leslie merely to conform to the difference in the shape of the co-operating casings or post; but the exact triangular cut of Leslie is shown in the same relative position in the Strauss British patent of 1892, and an equally analogous provision appears in Paxson’s patent of 1883 (No. 283,653) and in Waide’s patent of 1892 (No. 484,349).

. 4. In the patent granted to the appellee a locking mechanism is placed centrally between the posts, as in the Leslie patent; but it is of different construction, and not made automatic by the use of a spring, as shown in the Leslie lock. The function is identical, as it well may be wherever a lock is required; and, moreover, the Leslie lock is a mere duplication of his prior device. In the structure as manufactured by the appellee, this lock is so far changed that it serves to hold the back pieces from separation, and thus supplies the want of such provision in the mechanism of the posts. This provision is named by the experts on behalf of the appellant as “a third telescoping post, midway between the ends,” and stress is placed upon this device as performing the same function claimed for the Leslie telescopic posts in 'that regard, although obviously differing in the means employed, which is quite analogous to that shown in Waide’s patent, No. 484,349. It was, however, clearly open to the appellee, whenever it seemed desirable to hold the back pieces from separation, to adopt a simple expedient to that end, provided the specific means devised by the appellant was not so taken. A function not being patentable, the mere fact of the performance of this function by the new means operating in a new way cannot serve constructively to make it an infringement of the means not used, where the invention is of the limited character shown in this patent.

Paraphrasing the apt remarks which conclude the opinion by Mr. Justice Shiras in Boyd v. Hay-Tool Co., 158 U. S. 260, 267, 15 Sup. Ct. 837, 39 L. Ed. 973, if the patent in suit contained an invention entirely new, and first adapted to the ends sought, the differences shown in the appellee’s device and patent might be regarded as formal and evasive; but coming, as Leslie did, in the train of the numerous inventors that had preceded him, we must conclude that he is entitled only to the specific device shown, and this is not found in the appellee’s structure. Consequently no infringement is shown. The applications for both patents were pending in the patent office at the same time, and the decision of that office that no interference was found in the claims on the part of the appellee, and the subsequent grant of both patents, with the modifications in the Leslie claims as shown in the record, are strongly corroborative of this view of non-infringement; and, upholding such, view, it is unnecessary to pass upon the'question of the validity of the claims in suit. The decree dismissing the bill for want of equity is affirmed.