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The discussion may be confined within very narrow limits, and needs the statement of but very few principles of patent law. While the first and third elements do not appear in connection with the Driggs and Tasker extractor in the same form as with the Tasker, yet I think that they are accomplished by mechanical equivalents. An examination of the Patent Office shows that chambers for the breechblock, the mounting of the extractors in those chambers, and the application of the force to work the extractor to the end thereof away from the shell by means of the breechblock were well known ingredients at the date of the Tasker patent; and therefore the substitution of these ingredients in the last patent for the first and third elements in the former one affords no defense to the charge of infringement. (Seymour v. Osborne, 11 Wall. 516, 556; Gould v. Rees, 15 Wall. 187, 192, 193.) On the other hand, since neither of these elements contained anything new, the validity of the first claim in the Tasker patent must depend upon whether the second element therein, or the combination of all the three elements, contained anything new and useful.

If this claim be so construed that it does not embrace the curved surface of the slot against which the face of the extractor works, then I am of the opinion that neither the second element nor the combination claimed presented anything new, and that said combination was not therefore patentable. I reach this conclusion from a careful comparison of the extractor described in the Tasker patent with a British patent to Welin, No. 1329, issued in 1896, it appearing to me that every element embraced in the first claim of the Tasker patent, provided it does not embrace the curved face of the slot, is contained in the Welin patent. That the construction and operation of the two extractors may be readily compared, figures 4, 5, and 6 of the drawings of the Welin patent are reproduced below:

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The extractor a is provided with studs a', which are connected by links b and sleeve b? to the pin b', which is fast to the gun. This pin and sleeve project through a slot in the extractor, and the upper end of the extractor is provided with a roller a?, which engages the cam c on the breechblock carrier C. When the breech is closed the parts are in the position shown in figure 4. As the carrier is swung the cam c engages the roller a’ and rolls the nose of the extractor along the front wall of the face of the gun with a decreasing leverage until the sleeve b? reaches the other end of the slot a’, as shown in figure 6, when the fulerum shifts to this sleeve, causing a quick motion with a short lever arm.

I am unable to see any material difference between the movements of this extractor and the objects to be accomplished by those movements and those of the Tasker patent. This extractor has the curved surface at the toe and for some distance therefrom. The movement begins with the fulcrum on this curved surface, giving thereby a long leverage and slow action. Thus a powerful force is exerted to loosen the shell which has been highly heated and expanded by the explosion within the gun. The fulcrum shifts along this curved surface until the entire flat surface of the extractor is reached, when immediately the quick action caused by the change of fulcrum is produced.

The movements of the Tasker extractor are precisely the same except the rolling motion is continued some distance further along the surface before the quick action is producerl. That there is such quick action is shown by the following description in the specification of the final movement of the extractor:

“The extractor having rolled to the end of the curved surface in the gun may, if further movement is desired, pivot about its lugs in the guide-grooves in the position shown in figure 4, the claw E’ then moving slightly out of a straight line, but only due to the difference in direction of the arc subtending a small angle and the tangent thereto.”

This final action is, therefore, produced in the Welin patent by the extractor pivoting on the sleeve around the stud, which is fastened to the gun but protrudes through a slot in the extractor, and in the Tasker patent by the extractor pivoting on the lugs which are fastened to the extractor but move in grooves in the walls of the gun. In both instances it is this action which throws the shell from the gun after it has been loosened by the great force produced in the beginning by the fulcrum of the lever being on the curved surface near the toe of the extractor.

I am further of the opinion that on account of the very narrow basis upon which the Tasker patent rests, and the indefinite meaning of the expression “suitably shaped slot cut through its wall,” reference should be had to the specifications to determine what the character of the slot is which was intended to be used in connection with the extractor described, and that if a slot having a certain shape was regarded as essential to the proper operation of the extractor, the slot itself having the shape described should be regarded as an element of the combination claimed. It is well recognized that the specifications may be referred to to explain and restrict, but never to expand the claims. (Mitchell v. Tilghman, 19 Wall. 287; Stirrat v. Excelsior Manufacturing Co., 61 Fed. 980, 984; Adams Electric Ry. Co. v. Lindell Ry. Co., 77 Fed. 432, 449.)

By reference to the specifications and drawings it is seen that the curvature of the face of the slot is therein regarded as exceedingly important and, in fact, essential to the

proper working of the extractor. So much is this true that figure 9 is given for no other reason than to demonstrate that a point in a curved surface moving upon another surface with one-half the curvature of the former must move in a straight line. It is, moreover, essential that the claw of the Tasker extractor move in a straight line, or one deviating but little therefrom, provided the claw engages the rim of the shell, as shown in the drawings, as otherwise it would either become released from the shell or would jam it against the opposite wall of the bore of the gun.

It appears to me, therefore, that when the specifications and this first claim are carefully considered together, the curvature of the wall of the slot against which the face of the extractor works must be considered as an ingredient of the combination claimed. From the information before

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