401. That’s an error.

Your client does not have permission to the requested URL /books?id=TxKynbyaIAMC&dq=Instrument+Engineers'+Handbook&pg=PP1&ots=jvrdPR7wxJ&sig=1hOUpQQDQH_8drYjW1yPVocJSYI&hl=en&sa=X&oi=book_result&resnum=1&ct=result. That’s all we know.