PLANETARY SEASONS. 



the southern hemisphere during the other. "We enjoy by this 

 expedient the grateful succession of seasons ; it is thus that 

 spring, summer, autumn, and winter, follow each other with 

 pleasant variety, marking in their progress by obvious phenomena 

 the course of time. Yet this inclination or stooping of the 

 axis is so regulated that the extremes of the seasons are confined 

 within such moderate limits as are necessary and conducive to 

 the physical well-being of the numerous tribes which people the 

 earth. 



It is true that this succession of seasons was not indispensably 

 necessary to the continuance of the races that inhabit the earth, 

 for had the axis been perpendicular to the orbit so as to render 

 days and nights perpetually an/1 everywhere equal, the organised 

 world would still have continued to exist though subject to 

 certain modifications. 



25. Xow, on observing the position of the axis on which Mars 

 revolves, we find that it is inclined to the plane of the orbit of 

 that planet, at an angle of 28 27', not very different from that 

 at which the axis of the Earth is inclined to the ecliptic. The 

 seasons and climates of Mars are therefore similar to those of 

 the Earth. 



Observation has not yet determined the position of the axes of 

 rotation of Venus and Mercury, but it is probably not materially 

 different from that of Mars and the Earth. 



Thus we see that not only the same alternations of light and 

 darkness birt the same succession of seasons, regulated by nearly 

 the same limits of temperature, the same diversity of climates, 

 separated by nearly the same limits of latitude which prevail on 

 Earth, have also been ordained for those three planets. 



26. The atmosphere which surrounds the earth is an appendage 

 which has an obvious and important relation to the animal and 

 vegetable kingdoms. That respiratory beings depend on it for 

 the maintenance of their vitality is obvious. The mechanical 

 and chemical functions of the breathing organs is expressly 

 adapted to it. Its relation to vegetable life is not less important. 



But besides these qualities, without which life would become 

 extinct on the surface of the globe, the atmosphere administers 

 to our convenience and pleasures in other ways. It is the medium 

 by which sound is transmitted ; and as the apparatus of the 

 lungs is adapted to operate chemically upon it, so as to impart 

 to the blood the principle by which that fluid sustains life, so 

 the exquisite mechanism of the ear is constituted to receive the 

 effects of its pulsations and convey them to the sensorium to 

 produce the perception of sound. Again, the mechanism of the 

 organs of voice is adapted to impress on the atmosphere those 



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