delivered the opinion of the Court:

This is an appeal from concurrent decisions of the Patent Office tribunals awarding priority of invention to Perley E. Glass.

The issue is expressed iu three counts, of- which the following, count 1, is sufficiently illustrative:

“3. A machine for folding the edges of sheet material having, in combination, edge turning and loop-forming means, a ham*444mer, and an anvil having its face disposed obliquely to the body portion of the work.”

The earliest date claimed by William E. Lautenschlagor was March 21, 1913. Each of the three tribunals of the Patent Office has accorded Glass a prior date of conception, and has found due diligence thereafter on his part. The question is purely one of fact, and in such a case where, as here, there has been unanimity of decision in the Patent Office, the burden is heavily upon the appellant to establish error. To reach a conclusion in this ca,se different from that reached by the Patent Office, it would be necessary for us to discredit at least three witnesses, whose credibility is in no way impeached and whose testimony is reasonable and free from suspicion. This we cannot- do, for there must be a substantial basis for discrediting such witnesses.

It follows that the decision must be affirmed. Affirmed.