It is observable, that neither his diligence, unintermitted as it was, nor his want of books, a want of which he was, in the highest degree, sensible, ever produced in him that asperity, which a long and recluse life, without any circumstance of disquiet, frequently creates.  He was always gay, lively, and facetious; a temper which contributed much to recommend his learning, and which some students, much superiour in age, would consult their ease, their reputation, and their interest, by copying from him.

In the year 1735 he published Anti-Artemonius; sive, initium evangelii S. Joannis adversus Artemonium vindicatum; and attained such a degree of reputation, that not only the publick, but princes, who are commonly the last by whom merit is distinguished, began to interest themselves in his success; for, the same year, the king of Prussia, who had heard of his early advances in literature, on account of a scheme for discovering the longitude, which had been sent to the Royal society of Berlin, and which was transmitted afterwards by him to Paris and London, engaged to take care of his fortune, having received further proofs of his abilities at his own court.

Mr. Barretier, being promoted to the cure of the church of Stetin, was obliged to travel with his son thither, from Schwabach, through Leipsic and Berlin, a journey very agreeable to his son, as it would furnish him with new opportunities of improving his knowledge, and extending his acquaintance among men of letters.  For this purpose they stayed some time at Leipsic, and then travelled to Halle, where young Barretier so distinguished himself in his conversation with the professors of the university, that they offered him his degree of doctor in philosophy, a dignity correspondent to that of master of arts among us.  Barretier drew up, that night, some positions in philosophy, and the mathematicks, which he sent immediately to the press, and defended, the next day, in a crowded auditory, with so much wit, spirit, presence of thought, and strength of reason, that the whole university was delighted and amazed; he was then admitted to his degree, and attended by the whole concourse to his lodgings, with compliments and acclamations.

His theses, or philosophical positions, which he printed in compliance with the practice of that university, ran through several editions in a few weeks, and no testimony of regard was wanting, that could contribute to animate him in his progress.

When they arrived at Berlin, the king ordered him to be brought into his presence, and was so much pleased with his conversation, that he sent for him almost every day during his stay at Berlin; and diverted himself with engaging him in conversations upon a multitude of subjects, and in disputes with learned men; on all which occasions he acquitted himself so happily, that the king formed the highest ideas of his capacity, and future eminence.  And thinking, perhaps with reason, that active life was the noblest sphere of a great genius, he recommended to him the study of modern history, the customs of nations, and those parts of learning, that are of use in publick transactions and civil employments, declaring, that such abilities, properly cultivated, might exalt him, in ten years, to be the greatest minister of state in Europe.