He answered it the next day in a long and eloquent vindication which was oddly enough inclosed in a letter from his son, scarcely less than menacing. It begins--"My dear sir, You must conceive that your letter, combating many old ideas of my father's, and proposing many new ones, could not fail to set his mind at work, and to make him address the effect of those operations to you. I must, therefore, entreat you not to draw him aside from the many and great labours he has in hand, by _any further written communications of this kind_, which would, indeed, be very useful, because they are valuable, if they were conveyed at a time when there was leisure to settle opinions." Those are hard hits at the critic, but harder were still to come. "There is one thing of which I must inform you. It is, that my father's opinions are never hastily adopted, and that even those ideas which have often appeared to me only the effect of momentary heat, or casual impression, I have afterwards found, beyond a possibility of doubt, to be the result of systematic meditation, perhaps of years. * * * * The thing, I say, is a paradox, but _when we talk of things superior to ourselves_, what is not paradox?" He strikes harder still. "When we say, that one man is wiser than another, we allow that the wiser man forms his opinions upon grounds and principles which, though to him justly conclusive, cannot be comprehended and received by _him who is less wise_. To be wise, is only to see deeper, and further, and differently _from others_."