Atherton

This is an appeal from a decree dismissing a suit for infringement of letters patent No. 1,601,469, for an air register, primarily intended for use in a heating or ventilating system for buildings. The court below found that the device manufactured and sold by the appellee was in public use for more than two years prior to the date of the application for a patent; and, if this finding is supported by the testimony, the decree of dismissal was proper, whether the patent is void in its entirety or not.

The rule is well settled, of course, that a defense of this kind must be proved with certainty and beyond reasonable doubt; but whether the proof measures up to that requirement, or not, is ordinarily for the trial court to determine. An appellate court cannot interfere, unless it can be said as a matter of law that the testimony is legally insufficient to establish the defense with the requisite degree of certainty.

*76 The prior public use in this case was testified to by four witnesses, three of whom were without interest in the result. Three of the witnesses fixed the date of the prior use by reference to dates contained in deeds to which they were parties, and the fourth was…