THE PLANET MARS.

261

been lengthened by the present lunar tides to abont 1,400times twenty-four hours. The lunar tides would then for atime remain stationary ; but the solar tides continuing wouldstill further lengthen the Earth ’s day, so that it would at lastexceed its satellite’s month, as the day of Mars exceeds morethan thrice the month of its inner moon.

If there be any astronomers possessed of good telescopesupon Mars , there is little doubt that they can determinewhether its satellites are inhabited. It would, in fact, bejust as easy as it would be for us to determine the like ques-tion with regard to the Moon , if it were brought, in the twocases respectively, within about 1th or ^th of its present dis-tance. If, on the other hand, there are astronomers uponthose little moons, most wonderful must be the view of Mars which they enjoy! From the inner satellite its disc wouldsubtend an angle representing more than jths of the width ofthe whole heavens, i.e., nearly 424° ; while from the outer itwould still subtend an angle of about 161°, i.e., about T \th ofthe width of the celestial vault. The apparent area of its discin the two cases would respectively be about 6,400 and 1,000times that which our Moon presents to us ; its light some 400times as great when viewed from the outer satellite, and 2,500times as great from the inner one. And yet the sight wouldnot be so wonderful as that of Saturn to an observer placedupon the inner edge of its bright ring, at a distance of only18,000 miles from its surface, where its huge globe wouldsubtend an angle of about 844°.

Since the attraction of gravity upon the surface of Mars isonly about -jths of its value upon the surface of the Earth , wehave explained that any inhabitants upon it might well be two-and-a-half times as tall as ordinary men; but we can hardlyconceive how very huge those would have to be who should besuited to the smallness of the gravity upon these little moons.If their diameters are ^th of that of the planet, the attrac-tion of gravity upon their surfaces would be -tth of that uponthe surface of Mars, or about ^th of that upon the Earth ,supposing their densities to be equal to that of Mars . Wemay, however, remark that their density, and consequently the