In this case the General Electric Company, owner of patent No. 829,780, issued to Walter A. Hall, August 28, 1906, for an electrical transformer, charged Sutter and others with infringement thereof. The court below held the patent did not involve invention, and from a decree dismissing the bill the General Electric Company appealed to this court.

[1, 2] We find no ground to warrant our differing from the court below in that conclusion. Conceding the device was original with Hall, and that it involved economies of construction, a study of the testimony satisfies us of the absence of any and all of those features which ordinarily betoken invention. There was no recognized fault in transformers which the electric art was seeking to correct The necessity and advantages of open spaces in transformers were well known. Moreover, the prior art showed the advantage of keeping the transformer coils close together within the magnetic circuit and of separating them outside of it for ventilating purposes. Indeed, a study of the testimony shows that Hall’s device was simply the thoughtful work of a trained electrical, engineer who, when directed by his superior officer “to investigate to see what economies might be introduced as a result of modifying our practice, so as to use internal ducts in transformers of sizes of, say, 25 to 30 kilowatts,” did so; or, to quote the words of that officer:

“One of my assistants, W. A. Hall by name, was given the problem to investigate. After considerable study, he submitted designs and finally built a model along the lines that I have just described. The design was so much more efficient, and cost much less money than what he had previously used, that it was adopted and embodied in our regular production some time in the latter part of the year 1902.”

*282[3] The only novelty claimed by Hall in his patent ivas in substituting eccentric for concentric coil mounting, and the only advantage therein alleged was in economy of construction, and that the coils, instead of—

“being located concentrically, as heretofore, the two. outer coils are arranged so that a wider ventilating space is formed at one side of the core than at the other.”

The case, then, narrows down to the question whether the substitution in a transformer of eccentric for concentric coil mounting involved invention. In view of the fact that the general principles and practice of ventilating spaces in transformers were well known, and the desirability of keeping the transformer coils close together •within the magnetic circuit for electrical advantages, and of separating them outside the circuit for ventilating purposes, we cannot regard Hall’s eccentric coil mounting as other than simply an economical improvement, designed by an engineer skilled in that highly developed art.

The decree of the court below is affirmed.