But, although his knowledge in this field was of uncommon quality and amount, it does not seem to have surpassed his acquisitions in science. "I have attempted," he says in a striking passage, "with great diligence, to attain certainty as to what is needful to be known concerning the processes of alchemy and natural philosophy and medicine.... And what I have written of the roots [of these sciences] is, in my judgment, worth far more than all that the other natural philosophers now alive suppose themselves to know; for in vain, without these roots, do they seek for branches, flowers, and fruit. And here I am boastful in words, but not in my soul; for I say this because I grieve for the infinite error that now exists, and that I may urge you [the Pope] to a consideration of the truth."[35] Again he says, in regard to his treatise "De Perspectiva," or On Optics,--"Why should I conceal the truth? I assert that there is no one among the Latin scholars who could accomplish, in the space of a year, this work; no, nor even in ten years."[36] In mathematics, in chemistry, in optics, in mechanics, he was, if not superior, at least equal, to the best of his contemporaries. His confidence in his own powers was the just result of self-knowledge and self-respect. Natural genius, and the accumulations of forty years of laborious study pursued with a method superior to that which guided the studies of others, had set him at the head of the learned men of his time; and he was great enough to know and to claim his place. He had the self-devotion of enthusiasm, and its ready, but dignified boldness, based upon the secure foundation of truth.