IN the discussion that Dr. MacCormac's letter has elicited, the essential principle upon which the whole art of swimming is fundamentally based appears to have been overlooked. As Dr. MacCormac says, the human body naturally floats in water, and freely so in salt water; but how does it float, supposing the necessary condition of buoyancy, the inflation of the lungs, is maintained? If the limp, dead body of a man is thrown into water in this condition it floats with the head and face immersed, but with that part of the back just between the shoulders upwards, and just bobbing out of water. This is a drowning position, and the first business of swimming is to counteract the tendency to this position, that is, to balance the body in such wise that the head shall be upwards and the lower part of the face uppermost, in spite of the natural tendency of the head to sink, it having a greater specific gravity than water, or the average of the whole body. Dr. MacCormac, in his letter (p. 166), says that “it is just as easy, if we only knew it, to tread water as to tread earth”. Quite so; but it is also about as difficult. No human being can “tread earth” without training, the principal effort in this training being directed to keeping the centre of gravity within the base covered by the soles of the feet; and in like manner we must learn to keep the centre of gravity of the body and the centre of its buoyancy in a perpendicular line with mouth and nostrils in the air. I have been a swimmer since I was eight years of age, and consequently swim as naturally as I walk, and float easily in fresh or salt water, without any treading or paddling of any kind; but though I can thus lie basking luxuriantly and motionless, I am just as unable to sleep floating as to sleep standing upright. I have often tried, and immediately I begin to doze my mouth is under water. The effort of keeping the face upwards is as automatic and unconscious as that of standing still on the ground, but there is an effort of balancing nevertheless.