into the eye of the strut, and its threaded ends were passed through the slots in the ends of the compression member; the brake heads, which were provided with circular clamps or openings fitting the ends of the compression member, and with notches or depressions for the reception of the lugs on the caps, were slipped upon the ends of the compression and tension members; the threaded ends of the tension members were passed through the caps, which were placed upon the ends of the compression member; and suitable nuts were screwed upon the ends of the tension member. The result was a strong, light, simple, adjustable brake beam. Each brake head was prevented from moving along the beam by the tension member on one side and the cap on the other; the cap, beam, and brake head were securely locked together, and prevented from rotating upon each other by the engagement of the lug on the cap with the slot in the compression member and the notch in the brake head; a curve and a resilience could be imparted to the brake beam, and the face of the brake shoe could be coned to the tread of the car wheels by tightening the nuts upon the tension member; and this curvature, resilience, and coning could be maintained, adjusted, and regulated by the mere turning of the nuts on the ends of the tension member. The patentee claimed his combination in these words:

"(2) The combination, in a brake beam, of a hollow beam, a strut, end plugs or caps, 8, and a truss rod, 3, which extends through the caps, 8, and is provided with nuts, substantially as and for the purposes specified."

Some of the distinguishing characteristics of this combination are (1) its lightness, compactness, and simplicity, which result from the use of a hollow metallic beam and the passing of the ends of the tension member through the ends of the compression member, thereby combining the elements of the structure in a very limited space; (2) its constant adjustability by the mere turning of the nuts on the ends of the tension member, whereby the curvature of the beam, the coning of the brake shoes, the spring of the beam, and the rigidity or tension of the structure may be easily and speedily produced; and (3) its superior efficiency in practice, which is established beyond cavil by its extensive use.

After Hien had devised this combination, he discovered that the production and maintenance of a spring or resilience in the compression member made his combination far more efficient and useful than it had been without it. This resilience he produced by means of a combination, formed on the same principle as that described in his first patent, but differing somewhat in the forms of its elements and the details of its construction. These changes in forms and details are not secured by, and are immaterial to the consideration of, the three claims of his second patent which we are about to discuss, and for that reason they will be laid aside for the present. So far as the first, second, and seventh claims of the second patent are concerned, the resilience in the compression member was produced by tightening the nuts of the brake beam of the first patent until the compression member was so curved or bowed that it had a constant and strong tendency to spring back to its original position; and this resilience. was adjusted and perpetually maintained in use by the same means.

The capacity of this brake beam to produce and adjust the curvature and resilience of the beam and to cone the shoes to the tread of the wheels thereby, proved a determining factor in the success of Hien's invention. The resilience gave a perpetual tension and rigidity to his structure, which aided in preventing its deflection under the sudden shocks of the loads it was required to bear, and thus enabled it to meet the requirements of the railroad companies, while it locked the nuts upon the tension rods, since they could not turn under the strain which the spring of the beam imposed upon them, and all the parts of the structure remained securely fastened together. It was the union of this resilience of the beam, produced and maintained by means of the combination of mechanical elements claimed in his first patent with that old combination, which produced the successful brake beams that have now gone into such general use upon the railroads of the country. Hien undertook to secure this combination by his second patent. In the specification of that patent he described the means by which he produced the resilience. He carefully distinguished the spring of the beam, which he perhaps unfortunately called "camber," from a set camber or curve in a beam, and declared that the camber which constituted one of the elements of his combination was the adjustable resilience or spring of the compression member, produced and maintained by the use of the nuts in a combination similar to that described in his first patent. He claimed his second combination in these words:

"(1) A metallic brake beam, consisting of a compression member, a tension member, and an interposed strut; the compression member having a camber. and the beam structure containing means of adjustment whereby the camber of the compression member is produced and the resiliency of the beam made available.

"(2) A metallic brake beam, consisting of a hollow compression member, a tension member, and an interposed strut; the compression member having a camber, and the beam structure containing means of adjustment whereby the camber of the compression member is produced and the resiliency of the beam made available."

"(7) In a trussed brake beam, the combination of a tension member having threaded ends and nuts therefor, a strut, and a cambered compression member, which maintains the tension of the parts and prevents the rotation of the nuts, substantially as specified."

The brake beam described and claimed by Hien in his first patent, and that used by the appellee in these suits, are illustrated by the following drawings:

The only difference in the two devices is in the end plugs or caps, and consists in the fact that Hien's cap, which is shown by the figure marked "8" at the left of the drawing of his brake beam, has a re- . cessed nut seat, enters a short distance within the beam, and locks itself with the beam and brake head by means of a lug, while the appellee's cap does not enter the beam, has a raised nut seat, and locks itself with the brake head, which is fastened to the beam by a lug thereon, by means of shoulders on its periphery which engage with the corresponding projections on the end of the brake head. The form of the cap used by the appellee is illustrated by figures 3 and 4. The contention of the appellee is that the appellants are entitled to no relief in these suits, upon the four claims now under consideration, because (1) there was no novelty or patentability in the combinations they specify, and (2) if they were patentable, the claims were so restricted by the state of the art, by the proceedings in the patent office, and by the express terms of the claims that the doctrine of mechanical equivalents is inapplicable to them, and the brake beam of the appellee does not infringe upon the franchises they grant.

A patent is a contract by which the government secures to the patentee the exclusive right to vend and use his invention for a few years, in consideration of the fact that he has perfected and described it and has granted its use to the public forever after. The general rules for the interpretation of grants and contracts govern its construction, and the equitable principle that one who has derived great benefit from the performance of a contract ought not to be allowed to escape its burdens without cogent reasons is not inapplicable in its exposition. Among the primary rules for the construction of a contract are these: The court should put itself in the place of the parties at the time it is made, and should read its terms in the light of the facts and circumstances which then surrounded them. When the intention of the parties is manifest, it should control, regardless of inapt expressions and technical rules. In cases of doubtful validity or of ambiguous terms, that construction should be adopted which sustains and vitalizes the agreement, rather than that which destroys or paralyzes it. Prior negotiations are merged in the contract, and, while they may be considered to interpret its purpose, they must not

be permitted to contradict or modify its express meaning. Let us read and interpret these patents in the light of these principles.

A compliance with the first rule requires a knowledge of the state of the art of constructing brake beams when these grants to the patentee were made, and in reviewing its history the patentability of the combinations of Hien and the limitations imposed upon his claims by the state of the art when the patents were issued will be alike considered. Before entering upon the consideration of the state of this art in 1887, a few references, which cannot be permitted to affect either the validity or the scope of the patents, will be noticed and laid aside. On April 25, 1876, letters patent No. 176,522 were issued to George W. Eddy, and on November 15, 1887, letters patent No. 373,328 were issued to Joel F. Bales, for improvements in whiffletrees. The application for the latter patent was not filed until September, 1887, and the patent was not issued until November in that year, while Hien's first patent was issued on April 12, 1887. The patent to Eddy describes a trussed whiffletree, in which the ends of the truss rod and the ends of the tie rod are welded or riveted together and provided with threads for screws, by means of which caps having eyes for the traces are screwed upon the ends of the whiffletree. In the latter part of the specification of this patent a whiffletree that is said to be adapted for light draft is described, in which the ends of the truss rod, which are provided with threads for nuts, pass through the ends of the tie rod and receive caps, which are adapted to inclose the ends of the tie rod and to be screwed upon the ends of the truss rod until they bear against the ends of the tie rod. This construction differs from that of Ilien in that its caps are made to turn on the ends of the rods, instead of being securely locked against rotation as in the patents of the appellants. Regardless, however, of the similarity or difference of these devices the art of constructing whiffletrees, like the art of building bridges, is so remote from that of manufacturing brake beams for railway cars that trusses for either of the former purposes cannot be permitted to anticipate or limit the scope of the patents of the appellants. The circumstances under which trusses for bridges and for whiffletrees are to be used, the essential requirements of structures for those purposes, the functions they are to perform,— all these are so radically different from the circumstances, requirements, and functions which condition the use of railway brake beams that the efficiency and practicability of specific trusses for the former structures would not be likely to suggest to the skilled mechanic their use or their efficiency for railway brake beams. Trusses for the former purposes were neither designed, apparently adapted, nor actually used to perform the function of stopping railway trains, and the art which they illustrated was not in any way analogous to that in which the patentee, Hien, invented and used his combinations. A machine or combination which is not designed by its maker, nor actually used nor apparently adapted to perform the function of a patented machine or combination, but which is discovered in a remote art and was used under radically different conditions to perform another function, neither anticipates nor limits the scope of the patent. Ansonia Brass & Copper Co. v. Electrical Supply Co., 144 U. S. 11, 18, 12 Sup. Ct. 601, 36 L. Ed. 327; Topliff v. Topliff, 145 U. S. 156, 161, 12 Sup. Ct. 825,

36 L. Ed. 658; Potts v. Creager, 155 U. S. 597, 608, 15 Sup. Ct. 194, 39 L. Ed. 275; Westinghouse v. Air-Brake Co. (C. C.) 59 Fed. 581, 590; Walk. Pat. (2d Ed.) p. 54, § 68.

On May 19, 1898, one Hoffman, a witness for the appellee, testified that he built trucks in the Toledo shops of the Wabash & Western Railroad Company in 1874, and that he knew the kind of brake beams that were used on these trucks. He was asked to describe them, and he testified that they were trussed wooden brake beams, but failed to relate how the ends of the truss rod and the tie rod were attached to each other. He was taken to a car at Decatur, Ill., and shown a trussed wooden brake beam thereunder, in which the ends of the iron tension rod passed through the ends of the wooden brake beam, and through iron plates thereon, and were secured in place by nuts screwed upon their threaded ends, and was then asked if the brake beams he found on the trucks in 1874 were like this beam. He answered that they were. On cross-examination he said that the Wabash Railroad Company was not using in 1898 any brake beams of this kind, except on old cars such as had been retired. Wood, another witness for the appellee, made a drawing of this brake beam in 1898, and then the brake beam and the drawing were offered in evidence. A third witness testified that he was a carpenter, and was working on railway trucks for the Wabash Railroad Company at its shops in Toledo in 1874. The brake beam which had been found under the car at Decatur in 1898 was shown to him, and he testified that he recognized it, and that he had bored a hole in it in 1874. No drawing or plan of this or of any similar beam, made in 1874 or at any time prior to 1898, was produced. The claim of the beam itself to antiquity rests on the testimony of one witness that he identified a hole in it in 1898 which he bored in 1874, and the use of such beams by the Wabash Railroad Company at that time is sustained by the testimony of but one other witness to the effect that beams like this one were in use at that time. The solemn grants of great franchises cannot be stricken down by testimony so flimsy and unsatisfactory. The memory of men is too brief and fleeting, too easily swayed by chance and by interest, to permit the recollection of one or two witnesses, prompted by presently prepared pictures of the proof desired, to condition the validity of valuable patents that have stood unchal lenged for years. Unsupported oral testimony of a prior use is always open to suspicion, and it cannot prevail over the legal presumption of validity which accompanies the patent, unless it is suflicient to establish such a use beyond a reasonable doubt. The testimony relative to the use of this Wabash beam is not of that character, and it will not be further considered. Mast, Foos & Co. v. Dempster MillMfg. Co., 82 Fed. 327, 332, 27 C. C. A. 191, 195, 49 U. S. App. 508, 516; In re Barbed-Wire Patent, 143 U. S. 275, 12 Sup. Ct. 443, 450, 36 L. Ed. 154; Deering v. Harvester Works, 155 U. S. 286, 300, 15 Sup. Ct. 118, 39 L. Ed. 153; Miller v. Handley (C. C.) 61 Fed. 100, 102. For the same reason the evidence of the use in 1884 and earlier of a double trussed wooden beam on the Burlington Railroad must be disregarded. It consists of the testimony of three witnesses, a drawing bearing the date August 4, 1882, and several blue prints, which were evidently made after the patents to Hien were issued. No one