after making the foregoing- statement,delivered the opinion of the, court.
We are unable to find in the current regulator of the patent in suit anything more than an adaptation of the brush adjuster of the earlier patent. The two are essentially the same in mechanism, adjustment, motive power, and law of operation; and, in so far as the purposes intended or accomplished are not the same, they are distinctly analogous. The second patent purports to be only an improvement upon the first, “the method” of which is declared to be “adaptable to the present case of current regulation.” As first drawn, the specification declared the correspondence of Fig. 2 of the present invention with Fig. 2 of No. 228,659, with the explanation that, since a single pair of collecting brushes, when placed upon an obliquely-slotted commutator, replaces the double pair of the earlier design, the contact-making magnet, A, of that invention', is placed in the main circuit of the machine, so as to act substantially in the same manner as the magnet, i\f, in Fig. 1, of that patent; “that is, by variations of the main current.” By the specification, as it stands, the patentees say:
“As in our former invention, already referred to, the motor device used may be adapted to move by the current, or by the motive power, or by suita-*97l)lo clockwork, or by other mechanism adapted to be thrown in or out of action by an electro-magnet, and constitutes, as before, a minor feature of our present; system. Our present method of operating, so far as it relates to automatic regulation, is based upon the same principles of operation as our previous invention, and it consists in an improved construction and mode of use of the apparatus employed in patent No. 223,659.”
But, as the present method relates entirely to automatic regulation, it follows that, if the patent shows invention, it must be solely “in an improved construction and mode of use” oí a known apparatus, which, notwithstanding the improvement, is to operate upon the same principles as before. In just what feature of’the construction, or of the mode of use, the novelty and utility entitled to be called invention were supposed by the patentees to be found, is not specified and can only be inferred. According to the brief for appellant, “the improvement consists in discarding the accessory collector, with its intermittent, uncertain, feeble current, and unstable adjustment, and substituting the simple, practicable, and effective combination of the controller magnet, and main current.” “In both inventions,” it is said on another page, “the brushes are mounted on a rocking- yoke, so that the positions of their points of contact with the commutator can be shifted. In both of them the result sought is obtained by so shifting the brushes. In both of them this is accomplished by a motor mechanism which is automatically set into operation in one direction or the other, as the case may require, by a controller mechanism which acts in response to the abnormal conditions which are to be corrected. Here the similarity between them ends, and the dissimilarity, both in mechanical construction and mode of operation, begins. The taking away of the accessory collector changes the structure and introduces a new mode of operation, ⅞ ⅞ « for the reason that the current which actuates the controller magnet of the spark adjuster is not the main current, or any pari: of it, but a different current, derived from a different source.” In its last analysis, the argument for the appellant ends in this assertion, that magnet, A, of the earlier patent, is not excited by the main current of the machine, or a shunted portion thereof, hut only by a different current, derived from a different source, “flowing intermittently, and sometimes in one direction and sometimes in the other.” The truth of this proposition is disputed, and, though it is supported by the statement in the specification that “the accessory collector, C2, serves, as it were, the purpose of a feeler, the design of which is to test the electrical condition of the segments of the commutator at the moment of leaving the collectors, and to originate from that condition an adjustment of said collectors in whatever is necessary to secure efficient action,” it does not seem to follow, necessarily, that no current was intended to flow, or does flow, through the controller magnet, A, except that which results from the difference of potential between successive segments at the moment when the forward one passes from under the accessory brush. That is not declared to be an essential feature of the invention, and instruction is not given in the patent for■ so constructing the different parts of the combination, or for so proportioning the resistance in the main *98and accessory circuits, as to produce that result. On the contrary, the current through the accessory brush, it seems to be agreed (C. Q. 97, and answer, supra), “passes through a variation from a maximum to a minimum between the time of its first contact with each segment and its separation from that segment,” and, besides, it is shown to be a delicate, and, except with the experienced and skillful, a difficult work, to make an adjuster through whose controller magnet no portion of the main current shall-flow, and which shall be operative under the supposed intermittent or pulsatory current which is intended to be taken up by the accessory brush. Indeed, the objection urged against the experimental spark adjusters constructed by the defendants in professed conformity with Fig. 2 of patent No-. 223,659 is that the resistance of the accessory circuits was made so low as to permit the constant passage of a distinct part of the main current; and on that ground the experts and counsel of the appellant are agreed in asserting that the exhibits were really current regulators, embodying the invention of the patent in suit, and not the invention of the other patent. The uncontroverted testimony of Prof. Gross, examined in behalf of the appellant, is to the effect that it can be determined 'whether a brush regulator constructed in apparent conformity with Fig. 2, of patent No. 223,659, is in fact a spark adjuster under that patent, or a current regulator under the patent in suit, only by the experimental employment upon each apparatus of tests adapted to show whether or not an appreciable and effective portion of the main current passes through the accessory circuit This alone ought to be conclusive of the dispute. When such tests are necessary to distinguish one such device from another, it is manifestly an impracticable, not to say dangerous, proposition that the making or using of either under a given patent may be declared to be'an infringement of a different patent upon the other. It being admitted that, if the construction of a brush adjuster under No. 223,659 be such that a distinct portion of the main current will pass through the controller magnet, the device becomes a current regulator, it follows that, in respect to the question of invention, the omission of the accessory brush is of no significance. Its presence or absence does not affect essentially the mode of operation, nor determine the character of the device.
. But, waiving other considerations, we will assume that the 10 propositions of counsel for appellant are true; that the appellant’s theory of the process of short-circuiting is correct; that the accessory brush of No. 223,659 is not a member of a compound brush, designed to assist in the process of commutation, but a mere feeler, which finds and takes up the residual current or difference of potential which remains after imperfect work by commutator brushes proper. Does it follow that the current regulator of No. 238,315 is an essentially different device, working upon a different principle? We think not. The specification, as we have seen, says that the principles of operation are the same. In physical structure they are alike, and, both practically and .theoretically, they operate in like ways to effect like purposes. The proof shows, and it -was un*99derstood to be admitted at the bearing, that upon all dynamos which existed when the patents were issued the two devices were interchangeable, so that, when the brushes were moved so as to prevent spark, they established and maintained constant current, and vice versa. For all possible purposes then known, each device might have been called, with equal propriety, a spark adjuster (though that name is of later invention) or a current regulator. In dynamos of later construction, however, the points at which the brushes prevent spark and establish constant current are not coincident, as they were in the earlier machines; and, that being so, the brushes of a spark adjuster, it is conceded, will move to the place of no spark, regardless of current, while in the current regulator, responding to the current to be regulated, they will seek (he point of constancy regardless of spark; and hence, it is insisted, the two devices are essentially different in their modes of operation and in the purposes to be accomplished. The force of this reasoning is very much weakened by the further fact, which seems to be undisputed, that neither the adjuster nor regulator, when constructed according to the patent covering it, can be successfully used upon dynamos of irregular or nonuniform fields, in which the points of least spark and constant current are not quite nearly coincident. In order to avoid this difficulty, commutator brushes, applicable alike, as we conclude, to the brush adjuster of No. 223,659 and to the current regulator of No. 238,315, were devised, and so adjusted, as to have a variable spread, corresponding momentarily with the strength of that portion of the field within which the process of commutation should be going on. Both devices being capable of adap-(ation by the same means to dynamos of nonuniform field, and when so adapted effecting, as they did upon uniform dynamos, the same results, the inference is strengthened that, in their law of operation, as well as in mechanism, they are essentially identical. The discussion of the question has been varied and exhaustive, but, along whatever lines pursued, the argument has come back to the difference between the currents which are supposed to flow through the respective controller magnets. That difference we concede, but do not deem it controlling. One current is constant, the other is intermittent or pulsatory; but the pulsations are so frequent that the current seems to be constant, and its effect in energizing the magnet is the same as if it were. It differs practically from the main current only in strength. In order to be effective, it must be strong enough to cause the magnet to overcome the counteracting spring, or, conversely, that spring must be so weak as, at Ihe proper time, to be overcome by the strength of the magnet. If, instead of being in the accessory current, the magnet be transferred to the main current or a shunted portion thereof, exactly the same kinds of operation, effected in the same way and by like adjustments, must .go on. In both constructions, the levers, springs, coils, armatures, magnets, brushes, and dynamos are, or may be, the same; the electrical currents, whether coming from one part of the machine or another, are alike; and, acting by one and the same law, they differ only in *100volume or energy. The magnetic current, it may be said here, as in Western Electric Co. v. Sperry Electric Co., 7 C. C. A. 164, 18 U. S. App. 177, and 58 Fed. 186, is not itself a part of the device or invention, any more than a current of water is an element of a water wheel. The invention'is in the mechanism, not in the power which moves it; and, once a device has been patented, it is protected for all uses or functions of which it is found to be capable, whether anticipated by the patentee or not.
It is not difficult to suggest the employment of appliances for the control of water power in a way to illustrate not inaptly our- view of the present question. The water of a stream is accumulated by means of a dam, and, through head gates, is turned into a race or iiume, whereby it reaches and turns a wheel to which is geared the machinery of a mill or factory. That wheel, for the purpose of illustration, is the magnet, M, of the patents; the head gates are the commutator brushes,; and the water flowing through the flume or race is the main current. First, we will suppose that it is desired to maintain in the reservoir, by automatic means, a constant level or head, without waste or overflow at the dam. How shall it be done? With patent No. 223,659 before us, the answer is plain. It may be accomplished by such a construction of the dam that whenever there shall be an overflow the surplus will, by means of another flume and a head gate or valve, corresponding to the accessory brush, be turned .into and made to move a second wheel, representing magnet A, connected with suitable mechanism adjusted to lift or lower the head gates in the main current so as to effect the purpose of restoring the normal level in the reservoir. Theoretically, at least, head gates or valves in water flumes might be adjusted and controlled in that way. Next, we will suppose it to have been found desirable to establish constancy of current in the main flume or head race. How shall that be done? If constancy of ley el in the reservoir could be maintained, it is evident that the desired constancy of current would follow as effect follows .cause. They are coincident facts, and, if the coincidence could be permanent, no additional or different mechanism would be necessary. But the overflow current is intermittent, and sometimes feeble and inefficient. When the stream is swollen it is strong and lifts the gates too high; and if the stream runs so low that it becomes necessary for a time to- draw down the reservoir, in order to obtain the desired current in the flume, the overflow disappears and does not act at all. Does it require invention to devise a remedy? Clearly not. One familiar with the existing device could not fail to see that, in order to effect the new purpose, it was only necessary to make the controller wheel constantly and efficiently responsive to changes in the current to be regulated, just as Thomson and Houston, once they had found constant electrical current desirable, immediately proposed, as Prof. Thomson himself has testified, “to accomplish the necessary shifting or movement of the commutator brushes by automatic means in something the way that we had before used in adjustment through a limited range, only that we saw clearly that we must make whatever. *101small variations tlie current in tbe main circuit underwent, during tlie cutting out or on of lamps, act to control the position of tbe brushes through a considerable angle around tbe commutator; and this could be done by a sensitive magnet in the main circuit setting in motion, through contacts, a device which should do the main work of shifting the brushes.” In other words, it was only necessary to put magnet, A, in the main current, or a shunted portion of that current; ánd that, it was evident, could be done without any change of structure, except such as was necessary to cause a diminution of resistance in the accessory circuit, or an increase of the resistance in the main circuit, either of which could be accomplished in a number of ways explained by the witnesses. It was a plain case of mere adaptation of known means to a modified but analogous use. In the illustration supposed, the water wheel, in connection will) mechanism employed to move the head gates in order to maintain constancy of level and to -prevent overflow, may well have- been patentable as an original combination; but it is not an additional invention to turn into that wheel a. different or additional current, by force of and in response to which it will, by the same mechanism, move the gates or vahes over a wider range, if need be, to keep in the flume a constant current, Instead of a constant level in the reservoir. No new law or new mode of operation is brought into play, and, at most, only improved and enlarged action is effected.
Hut'the current regulator of the patent in suit, it is said, has gone into extensive use, and we are met with the usual inquiry, why, if there is no invention in it, did not somebody else make the same or like improvement upon the earlier construction? ' It would be enough to answer that if done by'anybody else than Thomson and Houston, or their assignee, it would have been an infringement of the first patent. However, it was done by Maxim, in whose patent., No. 228,543, the controller magnet is placed in the main circuit, and though the collector brushes moved thereby are not upon the commutator óf the dynamo from which the current of that circuit is derived, but upon a second dynamo, employed for the purpose of exciting the field of the first, the effect of the adjustment being to main-itiin a constant field and thereby to establish the desired constancy of current, the employment of the second dynamo does not disguise the fact of automatic regulation of the commutator brushes in the maimer and by the means, of the Thoinson-IIouston patents. If the patent now in suit should be upheld, it would be, in our opinion, an unwarrantable prolongation of the just monopoly conferred by the first patent, which, notwithstanding the strenuous efforts made to minimize it, we deem to have been of great merit, and entitled to liberal construction. Tbe decree below is affirmed.