“ The accustomed office of a writ of mandamus, when directed to a judicial officer, is to compel an exercise of existing jurisdiction, but not to control his decision. It does not lie to compel a reversal of a decision, either interlocutory of final, made in the exercise of a lawful jurisdiction, especially where in regular course the decision may be reviewed upon a writ of error or an appeal. ”

“ In the 6th section, as amended in 1910, that act declares: 'The jurisdiction of the courts of the United States under this act shall be concurrent with that of the courts of the several states, and no case arising under this act, and brought in any state court of competent jurisdiction, shall be removed to any court of the United States.' A like restriction upon removals appears in § 28 of the Judicial Code [36 Stat. at L. 1094, chap. 231, U.S.C.omp. Stat. Supp. p. 140] . ”

“ Like any other ruling in the progress of the case, it will be regularly subject to appellate review after final judgment, and the authorized mode of obtaining such a review, the action being at law, is by a writ of error. ”