Bishop Humphreys 's episcopate was one of marked activity, and even after his translation to Hereford , his interest in his native country did not lessen, although ill-health darkened his latter years. When dean of Bangor he improved the organization of the diocese , rebuilt the deanery , and joined bishop Lloyd in an effort to win back the Dissenters to the Church . In 1690 , he issued visitation queries in Welsh to find out the state of the diocese. He was the leading supporter of the S.P.C.K. in North Wales , and in a letter to the clergy he exhorts them to hold monthly meetings and to make themselves ‘ wholesome examples and patterns to the flock of Christ .’

An ardent Welshman , he merited Thomas Hearne 's tribute that ‘he was reckon'd next to Mr. Edw. Lluyd for knowledge in the British language; but Mr. Lluyd used to say he was a greater master of it.’ The bards , Edward Morris (d. 1689 ) and Owen Gruffydd ( 1643 - 1730 ) (qq.v.), wrote cywyddau in his honour, and the prose-writers Ellis Wynne , Edward Samuel , and Samuel Williams (qq.v.) acknowledged their indebtedness, the first and last by dedicating to him their works, Rheol Buchedd Sanctaidd and Amser a Diwedd Amser .

To Edward Lhuyd , the bishop was ‘ incomparably the best skill'd in our Antiquities of any person in Wales .’ James Tyrrell ( 1642 - 1718 ), the historian , accepted Humphreys ' chronology of the British princes and William Wynne ( 1671 - 1704 ) (q.v.) , dedicated his History of Wales to him. The heralds of the Colleges of Arms , Piers Maudit ( Windsor herald ), and Peter le Neve ( Norroy king of arms ), directed their enquiries on Welsh pedigrees to the bishop , who remarked to Maudit that searching out pedigrees was his chief diversion in spare hours.

Humphreys ' main literary work was his additions to and corrections of Anthony Wood 's Athenae Oxonienses , for the most part printed in Bliss 's edition of that work. Numbering over a hundred, these, together with a catalogue of the deans of Bangor and S. Asaph , provide a wealth of historical data for any considered history of the diocese. The bishop 's notes on Camden 's Britannia and on S. Winifride's Well , and his defence of archbishop John Williams cannot now be traced.