WORK AND PLAY. 137

“T am going,” said Dr. Newman, “to give you some
notion of the size, and distances, and orbits of the
planets, and you must try to imagine the picture as I
draw it. It is the illustration of a great astronomer.* —
Are you ready?”

“ Ready, sir.” |

“Now, suppose yourselves over a great green plain»
or prairie, miles across.” |

“Yes, yes, that is fine; go on, sir.”

“Tet it be very level and smooth, because our
planets must have free room for their rounds. In the
very centre of this plain, imagine a globe, two feet in
diameter. Call this globe the Sun.”

“ Ah! TI see it already,” exclaimed Carl.

“Wait a little, my boy; you don’t see it all yet.
Around this globe, let a grain of mustard-seed go round
and round, in an orbit one hundred and sixty-four feet
in diameter. The mustard-seed is Mercury.”

The boys laughed heartily at little Mercury, and
guessed he could scarcely be seen at that distance. |

“Next place a pea, going round a circle two hundred
and eighty-four feet in diameter. The pea is Venus.”

“T have seen it,” said Bob, “as the evening star.”

“Yes,” said the doctor; “and if you would only rise
a little earlier, you might see it as the morning star.
But we have a great way to travel. Here is pea
number two, which is—”

* Sir John Herschel: ‘ Outlines,” 1849.