VII. Are There Limits to Knowledge?

Modern Physics traces sensations back to processes of the smallest particles of bodies and of an infinitely fine substance, called ether, or the like. What we experience, e.g., as warmth is a movement of the parts of a body which causes the warmth in the space occupied by that body. Here again something imperceptible is conceived on the analogy of what is perceptible. Thus, the perceptible analog to the concept “body” is, say, the interior of a room, shut in on all sides, in which elastic balls are moving in all directions, impinging one on another, bouncing on and off the walls, etc.