Page:The Music of the Spheres.djvu/273

 th part as bright as the other satellites and is only 30 miles across.

In 1905 two other satellites were discovered by photography, still another in 1908 and another in 1914, making a retinue of nine satellites in all. These last two, which are very remote from the planet, were found to be revolving in the opposite direction from the other seven, which is from west to east, the direction that generally prevails throughout the heavens. Other exceptions to this rule are the outermost moon of the planet Saturn, the moon of Neptune and all four moons of Uranus. The ninth moon of Jupiter is about 15,400,000 miles from the planet and takes nearly 3 years to complete a revolution. Only 11 hours and 57 minutes for Barnard's satellite and nearly 3 years for the most distant one, is quite a contrast in periods. Although Jupiter's 5-hour night is rich in moons, he is not nearly as well supplied with moonlight as is the earth.

It has already been mentioned how, a Danish astronomer of the 17th century, discovered the finite velocity of light through the disappearance and reappearance of Jupiter's satellites within his shadow. This was later found true through direct experiment.

At least a peep at this mammoth and colorful world, with its bands and spots and swiftly moving satellites, should be the privilege of every man, woman and child.