... out of the shoulder, or the foot to be on the same level with the knee of the remaining leg. Sometimes, again, the position is vague; and sometimes it is ambiguous, as in another patient of ... black the outlines of the gray scrap, or by placing above the tissue paper another gray scrap of the same degree of brightness, and comparing together the two grays. On neither of them does the ... Similarly the draughtsman's immediate perception seems to be of the point of his pencil, the sur- [p. 38] geon's of the end of his knife, the duellist's of the tip of his rapier...