Percival was an earnest advocate of popular education. He manifested much interest in the first systematic attempt (at the instance of Mr. James Brewster) to furnish the people of New Haven with popular instruction in the form of lectures. At a public dinner, given by Mr. Brewster, on the occasion of opening the building in which rooms had been fitted up for these lectures, the late Mr. Skinner gave the toast, "Our mechanics, the right arm of New Haven," and Percival followed with, "Science, the right eye which directs the right arm of New Haven." He believed most fully in the superiority of intelligent labor. He pointed out cases in which a college-training had been connected with signal eminence in mechanical invention, and said, that, according to his observations, persons engaged in industrial pursuits usually succeeded in proportion to the thoroughness of their education. Percival himself gave a course of lectures, or rather, lessons, in New Haven,--not in the building above mentioned, for his natural timidity was too great to encounter a public audience, but in the theological lecture-room of Yale College. They were on the German language, and consisted chiefly of translations of prose and poetry into English, intermingled with philosophical commentaries on the peculiarities of the original. It was pure grammar; he did not talk German, and claimed no acquaintance with the niceties of pronunciation; but all his listeners, most of whom were graduates, were struck with his perfect mastery of the subject.