This case concerns Letters Patent No. 1,886,577, issued to Adolph Ousdahl, for a Coal Burning Apparatus, claims 21, 22, 24 and 26 of which are in issue. It also as brought concerned another Patent to Edgar T. Warner No. 1,912,876. The latter may be dropped from the discussion because the charge of infringement was not pressed. Plaintiffs asked for what was in effect leave to withdraw this part of the Bill without prejudice. We see no need to allow this motion and it is denied. The grant of the Patent is prima facie evidence of validity. Infringement was not proven and this part of the Bill may be dismissed on this latter ground. This protects the defendant from all charges of past infringement. We think this is just because the plaintiffs have subjected the defendant to the trouble and expense of preparing its defense and should either press the charge of infringement to a decision or abandon finally the charges made. The plaintiffs have their remedy for later infringements, if any.