His industry and perseverance were remarkable.  In none of his pursuits were these qualities more conspicuous than in his study of languages.  It cost him, especially, an almost incredible amount of labor to master French.  The slight elementary knowledge of this language which he acquired at Bentham cannot have given him so much as an insight into it; his acquaintance with it may be said to date from his visit to Congenies, when he had reached his fortieth year.  Yet, by indefatigable exertion, maintained during many years, he became able to write and speak it fluently, though, not correctly, and even to preach without an interpreter.  The difficulty which he encountered in the acquisition of languages, from the late period of life at which he commenced, was enhanced by his ignorance of Latin, that best trainer of the youthful faculties, and by a natural inaptitude for the memory of words.  A proof of the latter occurred when, with his quick-witted wife, he was occupied in conning over the Italian and Modern Greek Grammars, in preparation for their journey to the Ionian Islands.  The difference in their natural capacities in this respect is shown in her playful expression; “I got my lesson in half an hour; while John has been three or four hours over his, and does not know it yet.”

But although slow in study, he was quick and shrewd in the observation of actual life.  This was apparent in his daily converse; and it may also be continually traced in his Diary, where, describing those with whom he became acquainted in his numerous travels, he seizes, on the prominent feature of their mind or manners, and with a word affixes to each his own particular mark.  Of the hundreds of individuals who rise into view one after another in the course of these journeys, scarcely two are alike; a result which is, perhaps, due as much to the pen of the writer, as to the inherent diversities of the human character.

To this shrewdness of observation, he added a racy humor which those who knew him in his hours of relaxation and familiarity will not easily forget.  His mind was stored with quaint and pithy phrases, and apt illustrations, which he not unfrequently seasoned with his native idiom, the broad Barnsley dialect.  His north-country pronunciation, indeed, never entirely forsook him; and the singular graft of German which he made upon it during his residence abroad, caused it to be commonly supposed, by those who were strangers to his history, that he was a native of Germany.

The same moral constitution that enabled John Yeardley to pursue his objects with indomitable perseverance, sometimes betrayed him, as may easily be imagined, into a tenacity of purpose, bordering upon obstinacy.  To the same strength of will also, acting on the defects incident to a neglected education in early life, must be attributed those strong prejudices which were at times to be remarked in him, and of which he found it extremely difficult to divest himself.  But it was the triumph of grace, that whilst these faults of character and disposition remained for the most part only as a hidden thorn, the messenger of Satan to buffet him, the virtues to which they were allied, and all the faculties of his mind, were consecrated to the service of God and of his fellow-man, and his whole nature was enlarged, refined and elevated, by the all-powerful energy of the gospel.