to that of viewing a luminous ball two inches in diameter suspended
above Boston, by the telescope situated in the city of New York.
(Newcomb and Holden's Astronomy, p. 338.)

Phobos, the nearest moon, is only 4,000 miles from the surface of Mars,
and is obliged to move with such great velocity to prevent falling, that
it actually makes a circuit about its primary in only seven hours and
thirty-eight minutes. But Mars turns on _its_ axis in twenty-four hours
and thirty-seven minutes, so the moon goes round three times, while Mars
does once, hence it rises in the west and sets in the east, making one
day of Mars equal three of its months. This moon changes every two
hours, passing all phases in a single martial night; is anomalous in
the solar system, and tends to subvert that theory of cosmic evolution
wherein a rotating gaseous sun cast off concentric rings, afterward
becoming planets. Astronomers were not satisfied with the telescope;
true, they beheld the phenomena of the solar system; planets rotating on
axes, and satellites revolving about them. They saw sunspots, faculae,
and solar upheaval; watched eclipses, transits, and the alternations of
summer and winter on Mars, and detected the laws of gravity and motion
in the system to which the earth belongs. They then devised the
micrometer. This is a complex mechanism placed in the focus of a
telescope, and by its use any object, providing it shows a disk, no
matter what its distance, can be measured. It consists of spider webs
set within a graduated metallic circle, the webs movable by screws, and
the whole instrument capable of rotating about the collimation axis of
the telescope. The screw head is a circle ruled to degrees and minutes,
and turns in front of a fixed vernier in the field of a reading
microscope. One turn of the screw moves the web a certain number
of seconds; then as there are 360 deg. in a circle,
one-three-hundred-and-sixtieth of a turn moves the web one-three-hundred