sphere of definite dimensions, and consisting of the ethereal medium through which light, heat, electricity, and gravity are propagated. But are we to accept this definite sphere as the sum of the physical universe? Overwhelmingly vast it may appear to us, but shall we limit the creative power of the Infinite to a sphere which, compared to the infinitude of space, is as a mote in the sunbeam? But then the metaphysical question arises—and the ultimate problems of physics always merge in metaphysical questions — What is space? Is it an objective reality, or a subjective condition of thought? We cannot enter on this mare magnum of controversy, but we must advert to the curious correlations of time and space brought out by the laws of light.
From the simple law, that light requires time to travel from one point to another, it follows, that we see everything in the past. In the case of very distant objects, this leads to startling results. For every event in the past history of the world, there is a corresponding point in space, and if we were situated on a star at that point, we would, on looking down upon the earth, see the corresponding event transacted. For example, if we took up our position in a star, to which light would take six thousand years to travel from this globe, we would witness the scenes of paradise, and the roll of the world's history would unfold itself to our eyes. If the course of events appeared too slow, we could hasten it, in any degree, by glid-
