Relative Sizes:—
1. The Earth; 2. Jupiter; 3. Saturn; 4. Uranus; 5. Neptune.
XX.
THE PLURALITY OF WORLDS.
As soon as astronomy revealed the fact, that the planets are, in point of dimensions and density, worlds like our own, and that they, in like manner, share the influence of the sun,—the source and centre of the light and heat so essential to the existence of life,—the surmise was almost necessarily forced on the mind, that they might also be inhabited. Tins inference was too palpable to be long over-
