To put myself into a fair position with regard to Mr. Wall and your readers, I will reply to the latter part of his letter first, by stating that I endeavour to avoid all personality in this discussion, and should be sorry to descend to anything of the kind knowingly. When I spoke of "independency and consistency," I had not in view anything relative to his private character, but simply that kind of independence which enables a man to trust to his own powers of utterance for the expression of his ideas, instead of that incessant quoting the language of others, to which your correspondent, Mr. Wall, is so prone. As to his inconsistency, I mean that tendency which he exhibits to advocate a principle at one time, and denounce it at another. I shall prove that presently. Towards Mr. Wall, personally, I have neither animosity nor pique, and would take him by the hand as freely and frankly as ever I did were I to meet him at this moment. With his actions as a private gentleman I have nothing to do. I look upon him now as a controvertist only. So far, I hope I have made myself clearly understood by Mr. Wall and all concerned. I also should like to have had so important a question discussed without introducing so much of that frivolous smartness of style generally adopted by Mr. Wall. But, as he has introduced two would-be-funny similes, I beg to dispose of them before going into more serious matter. Taking the "butcher" first (see the fifth paragraph in Mr. Wall's last letter), I should say that, if I were _eating_ the meat, I should be able to judge of its quality, and know whether it was good or bad, in spite of all the butcher might say to the contrary; and surely, no man not an out-and-out vegetarian, or lacking one of the five senses--to say nothing of _common sense_--will admit that it is _necessary_ to be a "butcher" to enable him to be a judge of good meat. On the same ground, I contend that it is _not_ necessary for a man to be an artist to have a thorough knowledge of perspective; and I have known many artists who knew as little about perspective, practically, as their easel did. They had a vague and dreamy idea of some governing principles, but how to put those principles into practice they had not the slightest notion. I once met an artist who could not put a tesselated pavement into perspective, and yet he had some right to the title of artist, for he could draw and paint the human figure well. Perspective is based on geometrical principles, and can be as easily mastered by any man not an artist as the first book of Euclid, or the first four rules of arithmetic; and, for all that, it is astonishing how many artists know so little about the working rules of perspective.