QUÆRENS. I understood this fact already in our first conversation. [Sidenote: Retrogressive light pictures.] LUMEN. Well, suppose now that you remove from the Earth with a velocity _superior_ to that of light, what will happen? You will find again, as fast as you advance into space, the rays that set out _before_ you, that is to say the successive photographs which, from second to second, from instant to instant, project their rays into space. If, for example, you set out in 1867 with the velocity equal to that of light, you would retain for ever the year 1867 in sight. If you went more quickly, you would find before you the rays that had set out in former years, and which bore upon them the photographs of those years. In order further to illustrate this fact, reflect, I pray you, on the many luminous rays that have set out from the Earth in different epochs. Let us suppose the first to be at some instant of the 1st January 1867. At the rate of 300,000 kilometres a second, it has, at the moment in which I am speaking to you, already passed a portion of space from the instant of its departure till it reached a certain distance which I shall express by the letter A. Let us now suppose that a second ray sets out from the Earth a hundred years before, on the 1st January 1767; it is a hundred years _in advance_ of the first, and is found at a still greater distance--a distance that I shall express by the letter B. A third ray which I shall in like manner suppose on the 1st January 1667, is still _further off_ by a length equal to the distance that the light would travel in a hundred years. I call the place where this third ray reaches, C. Then a fourth, a fifth, a sixth, on respectively the 1st January 1567, 1467, 1367, &c., are posted at equal distances D, E, F, penetrating more and more into the infinite. Here, then, we have a series of photographs, taken on the same line, from post to post in space. Now, the mind which travels on in passing successively by the points A, B, C, D, E, F, can retrace successively the secular history of the Earth in those epochs. QUÆRENS. Master, at what distance are these photographs from one another? [Sidenote: Photographs of the life on Earth imprinted in space.]