In the ordinary "analytical geometry," the position and motion of all the points considered is referred to a rigid "body" or "frame of reference." This usually consists of an imaginary room of suitable size. The position of any point is then given by three numbers, i.e., its distances from one side wall and from the back wall and its height above the floor. These three numbers can only give one point, every other point having at least one number different. In four-dimensional geometry a fourth wall may be vaguely imagined as perpendicular to all three walls, and a fourth number added, giving the distance of the "point" from this wall also. Since "rigid" bodies do not exist in gravitational fields the "frame of reference" must be "non-rigid." The frame of reference in the Gaussian system need not be rigid, it can be of any shape and moving in any manner, in fact a kind of jelly. A "point" or "event" in the four dimensioned world is still given by four numbers but these numbers do not represent distances from anywhere; all that is necessary is that no two events shall have exactly the same four numbers to represent them, and that two events which are very close together shall be represented by numbers which differ only slightly from one another. This system assumes so little that it will be seen to be very wide in its scope; although to the ordinary mind, what is gained in scope seems more than that lost in concreteness. This does not concern the mathematician, however, and by using this system he gains his object, proving that the general laws of nature remain the same when expressed in any Gaussian coordinate system whatever.]220