through a small hole not more than 1/100th of an inch in diameter, the sky, the trees, houses, and nearly all the objects in an extensive landscape, occupying nearly an entire hemisphere, the light of all which may pass through this small aperture. 3. _Light is sent forth in all directions from every visible point of luminous bodies._ If we hold a sheet of paper before a candle, or the sun, or any other source of light, we shall find that the paper is illuminated in whatever position we hold it, provided the light is not obstructed by its edge or by any other body. Hence, wherever a spectator is placed with regard to a luminous body, every point of that part of its surface which is toward him will be visible, when no intervening object intercepts the passage of the light. Hence, likewise, it follows, that the sun illuminates, not only an immense plane extending along the paths of the planets, from the one side of the orbit of Uranus to the other, but the whole of that sphere, or solid space, of which the distance of Uranus is the radius. The diameter of this sphere is three thousand six hundred _millions_ of miles, and it, consequently, contains about 24,000,000,000,000,000,000,000,000,000, or twenty-four thousand _quartillions_ of cubical miles,--every point of which immense space is filled with the solar beams. Not only so, but the whole cubical space which intervenes between the sun and the nearest fixed stars is more or less illuminated by his rays. For, at the distance of Sirius, or any other of the nearest stars, the sun would be visible, though only as a small twinkling orb; and consequently, his rays must be diffused, however faint, throughout the most distant spaces whence he is visible. The diameter of this immense sphere of light cannot be less than _forty billions_ of miles, and its solid contents 33,500,000,000,000,000,000,000,000,000,000,000,000,000 or, thirty-three thousand, five hundred _sextillions_ of cubical miles. All this immense, and incomprehensible space is filled with the radiations of the solar orb; for were an eye placed in any one point of it, where no extraneous body interposed, the sun would be visible either as a large luminous orb, or as a small twinkling star. But he can be visible only by the rays he emits, and which enter the organs of vision. How inconceivably immense, then, must be the quantity of rays which are thrown off in all directions from that luminary which is the source of our day! Every star must likewise be considered as emitting innumerable streams of radiance over a space equally extensive, so that no point in the universe can be conceived where absolute darkness prevails, unless in the _interior_ regions of planetary bodies.