WILLIAMS », B., W. & 0. B. 00. 703 �ascertainment of damages was ordered to be mada by a master. �The master reports that the defendant, from December 19, 1865, to April 29, 1879, used continuously six lamps like the plaintifiPs lamp; that, from and including the year 1875 to April 29, 1879, it used five additional lamps, which vrere adjudged by the court to infringe, and whioh burned kerosene oil by reason of their infringing, on portions of the plaintiff's lamp; that during the time from December 19, 1865, to April 29, 1879, when the plaintiff's patent expired, the lamp pat- ented by him was the only one which could practically and Buccessfuliy burn kerosene oil, except such lamps as infringed said patent in whole or in part; that the lamp made and Bold.by John Carton, for buming kerosene oil, was not tho lamp described in his original or re-issued patent in evidence on the final hearing, but was an infringement on the lamp patented by the plaintiff; that, prior to the plaintiff's inven- tion, the only oils which were or could be practically and Buccessfuliy used in locomotive head-light lamps were lard, whale, sperm and kindred oils ; that the plaintiff's locomotive lamp was the first one which Buccessfuliy burned kerosejie oil; that since his said invention kerosene oil bas been ex- clusively used by railroad companies in their locomotive head-lights ; and that the defendant, by the use of the lamps adjudged to infringe the plaintiff's patent, was enabled to and did burn kerosene oil instead of the other and higher-priced oils above mentioned, which resuit was secured only by the use of the plaintiff's invention. �The report then states the average market priee of lard oil per gallon by the barrel for each year from and including 1866 to and including 1878, lard oil being the cheapest of the oils used in locomotive head-light burners except the plaintiff's, and those which infringed it; and also states the average market price of kerosene oil per gallon by the barrel for each of the same years. It also states that the 11 lamps were used by the defendant 20 nights in each month during said period of infringement, for four hours each night, kerosene oil being burned in them during the whole time; ����
