We need scarcely blame these men; at least we need not blame them overmuch. To say that they acted as they did is to say that they were human, were narrow-minded, and were the apostles of a lost cause. But _they_ could not know this; _they_ had no experience of the past to guide them; the conditions under which they found themselves were novel, and had to be met for the first time. Conduct which was excusable then would be unpardonable now, in the light of all this experience to guide us. Are there any now who practically repeat their error, and resist new truth? who cling to any old anchorage of dogma, and refuse to rise with the tide of advancing knowledge? There may be some even now. Well, the unpopularity of Galileo smouldered for a time, until, by another noble imprudence, he managed to offend a semiroyal personage, Giovanni de' Medici, by giving his real opinion, when consulted, about a machine which De' Medici had invented for cleaning out the harbor of Leghorn. He said it was as useless as it in fact turned out to be. Through the influence of the mortified inventor he lost favor at court; and his enemies took advantage of the fact to render his chair untenable. He resigned before his three years were up, and retired to Florence. His father at this time died, and the family were left in narrow circumstances. He had a brother and three sisters to provide for. He was offered a professorship at Padua for six years by the Senate of Venice, and willingly accepted it. Now began a very successful career. His introductory address was marked by brilliant eloquence, and his lectures soon acquired fame. He wrote for his pupils on the laws of motion, on fortifications, on sun-dials, on mechanics, and on the celestial globe: some of these papers are now lost, others have been printed during the present century. Kepler sent him a copy of his new book, _Mysterium Cosmographicum_, and Galileo, in thanking him for it, writes him the following letter: