THE PLURALITY OP WORLDS. 57 



stances which prepare us to expect some discrepancies in the provisions made 

 in these two groups ; but everything leads us to anticipate a uniformity in 

 each of them respectively. We shall on another occasion show that the 

 three planets, Mercury, Venus, and Mars, which with our own form the 

 inner group, do all turn on their axes ; that they have all a diurnal motion 

 completed in the same time, or very nearly so, as that of the earth. Thus 

 these several planets not only have days and nights, but have days and nights 

 precisely similar to our own. They are regulated by the same average dura- 

 tion ; and He that gave them those alternations has seen it good to " divide the 

 light from the darkness" after the same fashion. 



If, then, the duration of our days and nights be evidently regulated with a 

 view to the accommodation and well-being of the organized creatures to which 

 the earth has been appropriated, we are surely warranted by all analogy in con- 

 cluding that the adaptation of the same expedients in the planets, Mercury, 

 Venus, and Mars, have been directed to the same beneficent purposes, and that 

 the creatures upon them, as upon the earth, are so organized as to require the 

 same intervals of labor and rest, of activity and repose, of wakefulness and 

 sleep. 



In the outer group the times of rotation are different, yet among them a sim- 

 ilar uniformity prevails. Jupiter and Saturn revolve on their axes in about ten 

 hours'. The telescope has not informed us of the time of rotation of Herschel; 

 but it is probably not different from the two cognate planets. It appears then 

 that the intervals of light and darkness in these remote bodies, instead of being 

 regulated by intervals of twelve hours, is determined by average intervals of 

 five hours. A corresponding difference of organization and functions may of 

 course be inferred to prevail upon them ; but still it will be observed that the 

 difference between them and the inner group, lies merely in the duration of 

 intervals of light and darkness ; those intervals being in the main preserved. 

 There is no planet, then, in which are not provided days and nights. 



In considering the expedient by which days and nights are secured to the 

 planets, it is interesting to contemplate the particular position of the diameters 

 on which they have been made to turn. There are a great variety of different 

 diameters upon which the earth might have spun while it revolves round the 

 sun. It might, for example, have turned on a diameter at right angles to its 

 annual orbit. If it had been so we should have had equal days and nights 

 throughout the entire year, and at every part of the earth. It might again have 

 turned upon a diameter lying in the plane of its annual orbit. In such a case we 

 should not have had alternations of days and nights at all ; we should have had 

 the sun constantly visible for six months, and absent for other six months, mod- 

 ified in a very complex manner, however, by other vicissitudes ; in fact we should 

 have had changes of light and darkness utterly unfit for our wants. In the 

 first case we should have been deprived of seasons and of the means of main- 

 taining any convenient chronology. Thus, in either case, we should be strip- 

 ped of many of the benefits and utilities arising from the present arrangement. 

 Again, the earth might have turned upon an axis nearly perpendicular to the plane 

 of its annual orbit ; or in nearly that plane ; it might, in fact, be inclined in 

 any position, between those extremes. Had it stooped down nearly to the eclip- 

 tic, consequences would have ensued almost as fatal as those which any position 

 in the plane of the ecliptic would have inferred.' We find, however, in fact, 

 that a position has been given to this axis slightly inclined from the perpendicu- 

 lar. In virtue of this inclination the northern hemisphere leans toward the 

 sun during one half of the year, and the southern hemisphere during the other. 

 We enjoy the grateful succession of seasons ; it is thus that spring, summer, 

 autumn, and winter, follow each other with pleasant variety, marking in their 



