Satellites of Mars.

The night of August 11th, 1877, is famous in modern astronomy.  Mars has been a special object of study in all ages; but on that evening Professor Hall, of Washington, discovered a satellite of Mars.  On the 16th it was seen again, and its orbital motion followed.  On the following night it was hidden behind the body of the planet when the observation began, but at the calculated time—­at four o’clock in the morning—­it emerged, and established its character as a true moon, and not a fixed star or asteroid.  Blessings, however, never come singly, for another object soon emerged which proved to be an inner satellite.  This is extraordinarily near [Page 162] the planet—­only four thousand miles from the surface—­and its revolution is exceedingly rapid.  The shortest period hitherto known is that of the inner satellite of Saturn, 22h. 37m.  The inner satellite of Mars makes its revolution in 7h. 39m.—­a rapidity so much surpassing the axial revolution of the planet itself, that it rises in the west and sets in the east, showing all phases of our moon in one night.  The outer satellite is 12,579 miles from Mars, and makes its revolution in 30h. 18m.  Its diameter is six and a quarter miles; that of the inner one is seven and a half miles.  This can be estimated only by the amount of light given.

ASTEROIDS.

ALREADY DISCOVERED (1879), 192.  DISTANCES FROM THE SUN, FROM 200,000,000 TO 315,000,000 MILES.  DIAMETERS, FROM 20 TO 400 MILES.  MASS OF ALL, LESS THAN ONE-QUARTER OF THE EARTH.

The sense of infinite variety among the countless number of celestial orbs has been growing rapidly upon us for half a century, and doubtless will grow much more in half a century to come.  Just as we paused in the consideration of planets to consider meteors and comets, at first thought so different, so must we now pause to consider a ring of bodies, some of which are as small in comparison to Jupiter, the next planet, as aerolites are compared to the earth.

In 1800 an association of astronomers, suspecting that a planet might be found in the great distance between Mars and Jupiter, divided the zodiac into twenty-four parts, and assigned one part to each astronomer for a thorough search; but, before their organization could commence work, Piazzi, an Italian astronomer of Palermo, [Page 163] found in Taurus a star behaving like a planet.  In six weeks it was lost in the rays of the sun.  It was rediscovered on its emergence, and named Ceres.  In March, 1802, a second planet was discovered by Olbers in the same gap between Mars and Jupiter, and named Pallas.  Here was an embarrassment of richness.  Olbers suggested that an original planet had exploded, and that more pieces could be found.  More were found, but the theory is exploded into more pieces than a planet could possibly be.  Up to 1879 one hundred and ninety-two have been discovered, with a prospect of more.  Between 1871-75 forty-five were discovered, showing that they are sought for with great skill.  In the discovery of these bodies, our American astronomers, Professors Watson and Peters, are without peers.