THE PLANETS, ARE THEY INHABITED? 



other wants and capabilities of enjoyment which are periodical. 

 Thus they a,re capable of wakefulness for certain periods, after 

 which recurs the physical want of sleep. Now upon a general 

 survey of the creation, it is found that the average period which 

 must regulate the intervals of labour and rest, of wakefulness 

 and sleep, corresponds in the main with that which regulates the 

 alternations of light and darkness. 



In the vegetable kingdom we find prevailing also periodical 

 functions, certainly not so obvious and apparent, but not on that 

 account the less interesting, which are ascertained to have the 

 same close alliance with the period that regulates the returns of 

 light and darkness. Plants undergo certain changes and suffer 

 certain effects, in the presence of solar light, which are different 

 from, and in some respects contrary to, those which they undergo 

 in its absen-ce. These changes are essential to the vegetable 

 health of the creature ; without them the tribes of plants would 

 be extinct. 



16. The duration of these operations is just as essential as 

 their alternations. Light must be present a certain time, and 

 neither more nor less ; and its absence must be equally regulated 

 by limits, otherwise the plant must perish. There is, then, it is 

 evident, an essential relation between the functions and qualities 

 of the vegetable kingdom between the power of activity, the 

 susceptibility of enjoyment and the physical wants of animals, 

 and the periods which separate light from darkness ; but what* 

 are those periods ? What is the mechanical expedient to which 

 He has resorted to accomplish His inscrutable purposes, who 

 divided the light from the darkness, and "saw that it was good" 1 

 Nothing can be more simple. Nothing can be more beautiful. 

 Nothing can be more admirably perfect. While the globe of 

 the earth makes its annual course round the sun, it has at the 

 same time a spinning motion, on a certain diameter, as an axis, 

 in virtue of which it successively exposes all parts of its surf ice 

 to the light and warmth of the sun. Bach complete rotation, is 

 accomplished in the interval which we call twenty-four hours. 

 All points on our earth are alternately exposed to and with- 

 drawn from the solar light. The earth, in its annual movement 

 round the sun, is represented in Fig. 5. It will be seen that one 

 hemisphere is shone upon by the sun while the other is dark. 

 But as the globe revolves on its axis once in twenty-four hours, 

 each side is successively exposed to the sun's light and heat, 

 for average intervals of twelve hours. 



The culinary process of turning meat by a string or on a spit, 

 successively exposing every side to the heat of the fire, is a 

 homely illustration of this expedient. 

 10 



