[Illustration:  Fig. 41.—­Inclination of Orbits of Venus and Earth.  Nodal Line, D B.]

Fig. 41 shows a view of the orbits of the earth and Venus seen not from the edge but from a position somewhat above.  The point E, where Venus crosses the plane of the earth’s orbit, is called the ascending node.  If the earth were at B when Venus is at E, Venus would be seen on the disk of the sun, making a transit.  The same would be true if the earth were at D, and Venus at the descending node F.

This general view of the flying spheres is full of interest. [Page 108] While quivering themselves with thunderous noises, all is silent about them; earthquakes may be struggling on their surfaces, but there is no hint of contention in the quiet of space.  They are too distant from one another to exchange signals, except, perhaps, the fleet of asteroids that sail the azure between Mars and Jupiter.  Some of these come near together, continuing to fill each other’s sky for days with brightness, then one gradually draws ahead.  They have all phases for each other—­crescent, half, full, and gibbous.  These hundreds of bodies fill the realm where they are with inexhaustible variety.  Beyond are vast spaces—­cold, dark, void of matter, but full of power.  Occasionally a little spark of light looms up rapidly into a world so huge that a thousand of our earths could not occupy its vast bulk.  It swings its four or eight moons with perfect skill and infinite strength; but they go by and leave the silence unbroken, the darkness unlighted for years.  Nevertheless, every part of space is full of power.  Nowhere in its wide orbit can a world find a place; at no time in its eons of flight can it find an instant when the sun does not hold it in safety and life.

The Outlook from the Earth.

If we come in from our wanderings in space and take an outlook from the earth, we shall observe certain movements, easily interpreted now that we know the system, but nearly inexplicable to men who naturally supposed that the earth was the largest, most stable, and central body in the universe.

We see, first of all, sun, moon, and stars rise in the east, mount the heavens, and set in the west.  As I [Page 109] revolve in my pivoted study-chair, and see all sides of the room—­library, maps, photographs, telescope, and windows—­I have no suspicion that it is the room that whirls; but looking out of a car-window in a depot at another car, one cannot tell which is moving, whether it be his car or the other.  In regard to the world, we have come to feel its whirl.  We have noticed the pyramids of Egypt lifted to hide the sun; the mountains of Hymettus hurled down, so as to disclose the moon that was behind them to the watchers on the Acropolis; and the mighty mountains of Moab removed to reveal the stars of the east.  Train the telescope on any star; it must be moved frequently, or the world will roll the instrument away from the object.