He, every long vacation, read cosmographical lectures in the common refectory of the college. As this was an unusual thing, and he was very conversant in the subject, he gave great satisfaction to the auditors. The very first of these discourses, which he delivered towards the end of July, 1618, was so well approved, that he was elected Probationer-Fellow, and Moderator of the senior form in the Hall; and, on July 19, 1619, was admitted Perpetual Fellow. July 1, 1620, he was made Master of Arts. In the year ensuing he appeared in the character of a writer, when he set forth his Microcosmos: or, A Description of the Great World. The chief materials of this work were the abovementioned lectures. He began the composing of it on the 22d of February, 1619, and finished it on the 29th of of April following. It was first published in quarto, November 7, 1621. It was dedicated and presented to Prince Charles, who received it and the author very graciously. It was universally liked, and speedily bought up; so that, in 1624 it was reprinted in the same size, but with considerable additions, and again presented to it's royal patron. It was soon after put into the hands of King James, by Dr Young Dean of Winchester. His Majesty, at first view, seemed greatly pleased with it; 'till, meeting with a passage therein, where Heylin gave precedency to the French King, and stiled France the more famous kingdom, he was, forsooth, so exceedingly offended, forgetting how much more he had degraded both himself and the British nation, in the eyes of all Europe, that he ordered the Lord Keeper to suppress the book. Heylin was then at Oxford, whither Dr Young sent him notice of this untowards circumstance, perswading him to repair immediately to London, and endeavour the appeasing of his angry sovereign. But, by the advice of his friend Lord Danvers, who knew better how to estimate the King's wrath, he stayed where he was, and only wrote back to the Doctor an apology, wherein he declared that the error, in one of the exceptionable passages, was entirely the Printer's, who had put "is" instead of "was"; and that when he himself mentioned the precedency of France before England, "besides, that he did not speak of England as it then stood augmented by Scotland, he took what he did say from Camden in his Remains." James was hereby satisfied.