682 FBDEBAL EEPOBTEB. �from those existing when plain forward drivers are used. In regard to the alleged additional safety attendant uponthe use of the swing tmcks, there is the same difficulty. I am not convinced that there is any increased safety in running loco- motives with it. But if there is, there is no mater by which the value of that advantage, as a profit, can be measured, and during the argument the complainants disavowed any claim for profits on that account. �The case, therefore, is one for damages only. The evi- dence shows to my satisfaction that the complainants had a fixed royalty of $100 for each locomotive to which the invention was applied. The master adopted that as a proper standard for estimating the damages. In this I think he was justified by the case of Birdsall v. CooUdge, S Otto, 64. That, it is true, was an action at law. But there is no conceivable reason why the damages sustained by a patentee from the infringement of his patent are not the same whether he proceeds at law or in equity. Applying this standard, and adding interest to the royalties, the master has reported the damages to be $89,644, the invention having been used by the defendants in 614 engines. That sum will certainly cover ail the damages the complainants have sustained, and ail possible profits the defendants have made, if they made any. �A doubt arose in my mind at first whether interest should bave been addëd by the master to the aggregate of the royal- ties, but further reflection has removed the doubt. As I bave noticed, the royalties were allowed as the measure of damages. It is doubtless the general rule that interest prior to the final decree is not to be allowed upon profits or dam- ages, because, until the decree, they are unliquidated. Mowry V. Whitney, 14 Wall. 653. But the rule is not without excep- tions. We said in that case: "We will not say that, in no possible case, can interest be allowed." The present seems to be one not within the reason of the rule, and therefore proper for an exception. The damages cannot be said to have been unliquidated from the first. The amount of the royalty was fixed when the defendants began to use the inven- ����
