THE PLANETS, ARE THEY INHABITED ? 



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

 regulated with a view to the accommodation and well-being of 

 the organised creatures to which the earth has been appropriated, 

 we are surely warranted by all analogy in concluding that the 

 adaptation of the same expedients in the planets Mercury, Venus, 

 and Mars, has been directed to the same beneficent purposes, 

 and that the creatures upon them, as upon the earth, are so 

 organised as to require the same intervals of labour and rest, of 

 activity and repose, of wakefumess and sleep. 



23. In considering the expedient by which days and nights are 

 secured to the planets, it is interesting to contemplate the parti- 

 cular 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 such had been the case we should 

 have had equal days and nights throughout the entire year, and 

 at every part of the earth. 



If its axis, as it might have been, had been in the plane of 

 its annual orbit, the sun would have been constantly above 

 the horizon for an interval of several weeks in summer, and con- 

 stantly below it for a like interval in winter. The duration of 

 these intervals of incessant light and incessant darkness would 

 have varied in different parts of the earth, increasing with the 

 latitude. No diurnal alternations of light and darkness would 

 take place except for a short interval before and after the 

 equinoxes. 



It is not necessary to enlarge upon the consequences of such 

 an arrangement, to render it apparent that they would be utterly 

 incompatible with the well-being, and perhaps even with the 

 maintenance, of the organised world. 



In the first of the cases here supposed, we should have been 

 deprived of the seasons sind of the means of maintaining a con- 

 venient chronology, and in both cases we should be stripped 

 of many of the benefits and utilities arising from the present 

 arrangement. 



k But, between these extreme possible positions of the axis 

 of rotation, there are a,n infinite variety which would have been 

 nearly as unsuitable. Had the axis leaned down nearly to the 

 ecliptic, consequences would have ensued almost as fatal as 

 those which a 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 perpendicular, as 

 represented in fig. 5. In virtue of this inclination the northern 

 hemisphere leans toward the sun during one half of the year, and 

 14 



