Measured by all standards, the things which Koppers did involved invention, if he was the first to do them.

But the defendants say, that in multiplying regenerators, in changing their position, and in connecting them directly with the heatingchambers, Koppers was not the first to do these things, citing as anticipations, first, the published report of the Fiftieth Congress of the Technical Society of the Gas Industry of France, held June 24, 1878, at Paris, on the subject of the Paris gas-retort furnaces; and, second, Dods U. S. Patent No. 571,558-1896, for a gas generator.

The fundamental difference between these references and the invention of the patent in suit-which we observe on the threshold and which we shall keep in mind throughout the discussion without burdening this opinion with repeated allusions to it-is the difference in the arts to which the references and the invention of the patent respectively belong. Paris gas-retort furnaces and the Dods gas generator belong to an art fairly described by their names, in which gas is the main product and coke the by-product. It may be termed the art of by-product gas-ovens. The invention of the patent belongs to an art in which coke is the main product and gas the by-product. This is the art of by-product coke-ovens.

[1] Though the two arts, producing the same products from the same source, are concededly related, yet differences in them, if fundamental, may validly prevent inventions in one from operating as anticipations of inventions in the other. While distillation of coal is practiced in both arts, and, therefore, coke-ovens or coking-chambers are included in the organization of both, difference in the process of distillation, in the function of the ovens, and in the products sought and obtained, mark the difference in the arts. The issue of invalidity of an invention in one art because of anticipation by inventions in another art, when the arts are different, though related, must be determined with a cautious regard to the differences that distinguish the two.

The Paris gas-retort contains coking-chambers, and regenerators, or recuperators, for preheating air. The coking-chambers are in the form of semi-cylindrical or tubular retorts, which lie horizontally across the furnace structure, each holding several hundred pounds of coal. These tubular coking-chambers are stacked in rows in what is substantially a flame-filled heating-chamber, in which flames are diffused throughout the chamber, above, below and around all parts of the coking-retorts. The system employed to preheat air for combustion is without reversal in the direction of flow and without alternate change of position of the flames. While coke is a product of the Paris gas-retort, it is incidental, the main object of the Paris gasretort being the production of gas. In this furnace, there is nothing that requires uniformity of heat distribution, and therefore there is no means to perform that function. In a furnace of this type, the problems of a by-product coke-oven are not present, and, as we regard it, there is nothing in it to suggest the means which Koppers 28 years later employed to solve such problems.

The Dods gas generator (U. S. No. 571,558-1896) comprises com

(258 F.)

bustion-chambers, heating-chambers, and and regenerators. Heatingchambers and combustion-chambers are intermediate one another, as in coke-ovens, and regenerators (two in number) are placed below each heating-chamber. The prior art coke-oven system of reversing the flow of preheated air for combustion and of waste gases for reheating regenerators is used. On first view, Dods' organization seems to resemble rather closely the invention of Koppers. On examination, however, it is seen, that the coking-chambers of the Dods gas generator are tapered and in position are steeply inclined, the broader end of the tapered chamber being lower than the upper end; and that the intermediate heating-chambers are of similar dimensions and positions. These heating chambers are open in the sense of being without flame-flues to confine combustion to a particular direction or to control its distribution. As the furnace is a gas-retort, its primary product being gas, there is neither need nor means for the uniform distribution of heat.

[2] The pairs of regenerators under the heating-chamber are stepped one above the other and so are out of parallel with the inclined heating-chambers. Connections between regenerators and heatingchambers for the passage of preheated air are long and unequal conduits. This inequality of delivery conduits, we are told, makes uniform delivery of preheated air impossible. Gas is delivered to the heating-chamber by gas conduits of unequal length parallel with the air conduits, and combustion takes place on the meeting of gas and air in the open heating-chamber. These limitations, we are shown by the testimony, conflict with any practice of coke-oven distillation. As Dods' invention has never reached the industries-although it preceded Koppers by ten years-we do not know whether it is operative. We are inclined to believe, because of its lack of means for uniform heat distribution, that it will not produce metallurgical coke or those by-product gases which are destructively decomposed by overheating and are recovered only by uniform heating. We cannot believe that either the Paris gas-retort furnaces or the Dods gas generator did the things which Koppers did when he invented the cokeoven of his patent, or that they suggested to Koppers the conception which later he put into practice. Therefore, we agree with the learned trial judge, that the Paris gas-retort furnaces and the Dods gas generator do not anticipate Koppers' invention, and find with him that claims 1 and 5 of the Koppers patent in suit are valid.

We shall next direct our discussion to the issue of infringement of the Koppers patent in suit.

The defendants' alleged infringing by-product coke-ovens were built under patents to Wilputte (U. S. Nos. 1,212,865, 1,212,866-1917). Wilputte, like Koppers, made free use of what he found in the artwith this difference: He found Koppers there. Wilputte took the combustion organization of the upper story of the prior art by-product coke-oven and embodied it in his oven without change, except the elimination of the bus-flue. Koppers cannot complain of this, for he did the same thing. Wilputte's changes, like Koppers', were made in the organization of the lower story. Unless these changes were

his conceptions, the question is: Where did Wilputte get them? From Koppers or from the prior art?

The elements of the Wilputte oven are elements of the prior art. Their organization, confessedly, is not the organization of the prior art. Then whose organization is it? The plaintiff admits that in certain structural details Wilputte differs from Koppers, but contends. that, basically, it is the organization of the Koppers invention. The defendants admit similarity in certain structural essentials, but insist that the organization involves a fundamental difference-conceived by Wilputte-which makes infringement of Koppers impossible. In order to compare the Wilputte oven with Koppers' and to distinguish the two, on the issue of infringement, it is necessary to show the principal characteristics of the construction and operation of the Wilputte oven. An examination of diagrams of the last Wilputte patent, here inserted, will, on comparison with diagrams of the Koppers patent, previously inserted, be of assistance.

Externally and considered as a unit, the Wilputte oven is not distinguishable from Koppers. There is no infringement here, for in this respect Koppers is scarcely distinguishable from the prior art. Internally, and considered with reference to its duality of organization, the Wilputte oven is not different from Koppers. Here again there is no infringement, for in this Koppers copied the prior art. The conbustion organization of Wilputte, located in the upper story of the oven, is the same as that of Koppers, but as Koppers took this organization from the prior art, it was equally free to Wilputte. The issue of infringement begins at the point where Koppers left the art and began to make changes. This is in the organization of the lower story

and in the connections between the organizations of the two stories of the oven. Wilputte's first change, like that of Koppers, was in the number of regenerators, the change being from a set of two to a number equal to the number of heating-chambers. His next change, like that of Koppers, was in the position of the regenerators from longitudinal of the oven to crosswise the oven and from right angles with the heating-chambers to a position below and parallel to them. Wilputte's last change, like Koppers', was from an indirect connection between the regenerator and bus-flue of each heating-chamber to a multiple direct connection between regenerator and heating-chamber. Assuming this comparison of the two ovens to be correct so far as it goes, claims 1 and 5 of the Koppers patent read literally on the Wilputte structure. To avoid the legal consequence of such reading, Wilputte distinguishes his structure from Koppers by specifying a difference in the position of the regenerators with reference to the heating-chambers and by indicating a difference in the types of regenerators and in their mode of operation.

It is conceded by the plaintiff, that if the regenerators of the Wilputte oven are longitudinal of the oven, Willputte does not infringe. Koppers. This, the defendants maintain, is the case. The first phase of the issue of infringement, therefore, is the position of the Wilputte regenerators.

Viewed as a regenerator extending crosswise the oven, the Wilputte regenerator is the Koppers regenerator substantially in size and dimensions and actually in its location below and parallel to the crosswise heating-chamber. The claimed difference is this: Koppers' regenerator is an unitary structure, while Wilputte's regenerator is divided into twenty-eight compartments by partitions extending from the sole

channel to the top. Again like Koppers, the Wilputte regenerators are made into a battery of any desired number, extending from the front to the back of the oven. In the battery of Koppers' regenerators. each regenerator is divided from its neighboring regenerator by the supporting walls of the oven. The same is true in Wilputte, with the difference that in the latter there are spaces left open in each supporting wall between all regenerators, the spaces being equal in area to that of two bricks. These spaces are termed "equalizing ports." As these wall-slits or equalizing ports appear in each supporting wall, they leave openings longitudinal of the entire oven. The defendants. maintain, first, that the frontal splitting up of the (Koppers) cross-regenerator into multiple compartments makes the partition of each compartment the side of a smaller regenerator, and, second, that the sequence of wall-slits or equalizing ports, being longitudinal of the battery, gives the Wilputte compartmental regenerator a position longitudinal of the battery and not crosswise, and that, in consequence, the regenerator so shaped and positioned is in effect a reversion to the prior art and avoids infringing Koppers.

Elaborate argument was made on this contention. We shall not discuss it in this opinion, because we are satisfied that the inconsiderable openings in the supporting walls between the Wilputte compartmental regenerators do not make the position of the regenerators longitudinal; nor do they make them functionally longitudinal, because under normal conditions, when air is driven into each regenerator compartment by fans and drawn through the regenerator by smokestack draft, the equalizing ports have nothing to equalize and perform no function. Air thus driven and drawn naturally moves upward in each regenerator without stopping to pass laterally through the equalizing ports. In fact, the whole theory of difference between Wilputte and Koppers in mode of operation is based on the fact that into each regenerator compartment of the Wilputte oven a dose of air is fed precisely equal to the capacity of that compartment. This equality of dosage makes the equalizing ports functionless, under normal conditions.

The sole-channel is as certainly a part of a regenerator as the checkerwork of firebricks. The brick checkerwork cannot heat air until air is brought to it. It is the function of the sole-channel to bring unheated air to the regenerator and to feed it at multiple points to the checkerwork above, there to be heated. As the sole-channel is a part of a regenerator, the direction of the sole-channel is a fair indication of the position of a regenerator. The sole-channel of all regenerators of the prior art (also in Koppers) is lengthwise the regenerator, whatever the position of the regenerator with reference to heating-chambers; and so in Wilputte, the sole-channel, or its equivalent, is crosswise the oven and lengthwise the regenerator, passing under and serving unheated air to its many compartments.

For the reasons we have indicated, without elaborating them, we are clearly of opinion, that the Wilputte regenerators are not longitudinal of the battery, but are crosswise, and in this position they follow Koppers.