Page:The evolution of worlds - Lowell.djvu/147

Rh kind of comet. Nearly a year rolled by before Lexell showed by calculation of its motion that it was no comet, but undoubtedly a new planet beyond Saturn travelling at almost twice that body's mean distance from the Sun.

By reckoning backward, it was found to have been seen and mapped several times as a star,—no less than twelve times by Lemonnier alone,—and yet its planetary character had slipped through his fingers. It can even be seen with the naked eye as a star of the 6th magnitude, and its course is said to have been watched by savage tribes in Polynesia long before Sir William Herschel discovered it.

Its greenish blue disk indicates that it is about thirty-two thousand miles in diameter, and its mass that its density is about 0.22 of the Earth's or, like Jupiter's, somewhat greater than water. Of its surface we probably see nothing. Indeed, it is very doubtful if it have any surface properly so called, being but a ball of vapors. Its flattening, $1⁄11$ according to Schiaparelli, which is probably the best determination, agrees with the density given above, indicating its substance to be very light. Belts have faintly been descried traversing its disk after the analogy of Jupiter and Saturn. These would be much better known than they are but for the great tilt of the planet's axis to the ecliptic, so that during a part of its immense annual sweep its poles are pointed