LOCOMOTIVE SAFETY TEUOK CO. V. P. E. 00. 681 �according to the rule in Mowry v. Whitney, be liable only for the advantage they had in that use over what they would bave had in case they had used a combination of an engine with forward driving-wheels without flanges, and witb a rigid truck. I cannot see that what they had in use in 1866 haï any bearing upon their liability to account for profits made in 1867 or 1868, when they resorted to the complainants' invention. If a man, making boards by hewing them from logs by an adze, changes bis mode of manufacture to the unlicensed use of a patent rotating saw, it wonld be a strange doctrine to hold that he is responsible for ail the increased advantages of one mode of manufacture over the other. Neither Mowry v. Whitney, nor any other decision witb whicb I am acquainted, justifies any such accounting. Mowry was held liable to account only for the advantage his useof Wbit- ney's process gave him over other knôwn modes of making car wheels, equally valuable and salable in the market, though it did not appear those other modes had ever been used by the infringer. In accounting for profits, as such, for which an infringer is liable, the sfcate of the art when the invention was made is always to be considered. �But were it conceded that the defendants in this case did se- cure some advantage from the use of the complainants' patented device, instead of other devices they were at liberty to use, (which I am unable to perceive, ) I tbink there is not suflicient in the evidence to enable me to make any reliableestimate of the value of that advantage. The defendants are not to be held liable for profits in any amonnt unless there is some satisfac- tory evidence that profits to that amount were made, though they may be answerable in damages for their invasion of tho complainants' right. Some witnesses, it is true, bave given estimates of the saving of wear by the use of the swinging truck. But an examination of their testimony convinces me that their estimates are mere guesses, without any reliable basis. There are no facts in evidence to justify them. Besides, the comparisons upon which they rest their conjectures are inad- missible in view of what I bave said. They rest upon thô supposed wear of tires or flanges under different conditions ����
