“ The difference between the two modes of securing a review, as contemplated by the statute, lies in the fact that a writ of error is granted as of right, while a writ of certiorari is granted or refused in the exercise of a sound discretion. ”

“ In addition to mining coal in Pennsylvania, the defendant was doing business in New York and, conformably to the laws of the latter state, had designated an agent therein upon whom process against it might be served. ”