The question of infringement in this case depends upon the result of the inquiry whether the defendant employs the arc, as distinguished from the incandescent, principle in its electric furnace in the manufacture of calcium carbide. The burden is upon the complainant to establish by .a fair preponderance of testimony—and not by mere scientific speculation—that the defendant does use the arc. We are, however, not entirely satisfied that the complainant has sustained this burden, and accordingly feel constrained to affirm with costs the decree of the Circuit Court upon the opinion of the judge holding it; and it is so ordered.