THE MAJOR PLANETS. 255 



i incompatible with the existence of physical arrangements similar to those 

 ( i which prevail upon the earth ; such inferences are, as we conceive, premature 

 and unfounded. They are based upon the supposition that the temperature 

 depends solely upon the uensity of the solar rays. Now we have noticed else- 

 where the fact, that other agencies are concerned in the production of tempera- 

 ture, and have given as an example all the varieties of temperature which pre- 

 vail between the tropics at different elevations. 



In the valleys and planes of these regions, we find their proper climate; as- 

 cending the tropical ranges, at great elevations we encounter all the vegetable 

 phenomena of temperate climates, and at still greater elevations we arrive at a 

 temperature as rigorous as that at the poles. How easy is it, then, to conceive 

 atmospheres and geographical arrangements provided on other planets, which, 

 combined with the peculiar intensity of solar light and heat, shall produce 

 a result which will fix the general temperature of any of the planets within the 

 same limits that restrain it on the surface of the earth. 



NEPTUNE. 



This is the most remote and the latest discovered of all the large planets. 

 The extraordinary circumstances attending its discovery have given to this planet 

 a special interest. After the discovery of Uranus, efforts were made to reduce 

 its motions to the known laws of gravitation, but they were found to be very 

 irregular, and seemed to be under some unknown influence. Many were dis- 

 posed to attribute these irregularities to a relaxation of the rigorous laws of gra- 

 vitation in those distant regions of space, while others conceived the possible 

 existence of a remote undiscovered planet, whose attraction drew Uranus out 

 of its regular orbit. 



Leverrier, an astronomer of Paris, determined to investigate these irregular- 

 ities, and, if possible, discover the unknown planet which caused them. He 

 first calculated the disturbing influence of all the known bodies in the solar 

 system. This did not account for all the deviations of Uranus. He therefore 

 pursued his investigations ; calculated the distance, mass, inclination and revo- 

 lution of the unseen planet, and on the 31st of August, 1846, read a memoir 

 of the results before the Academy of Sciences ; even pointing out the place in 

 the heavens where the strange planet would probably appear. This wonderful 

 account excited the greatest interest among astronomers, yet, such was the 

 difficulty of the problem, that few could believe the prediction These misgiv- 

 ings were soon dissipated. On the 1st of September, Leverrier wrote to Dr. 

 Galle of Berlin, asking him to direct his telescope to that point in the heavens 

 where he supposed it to be. On the very first evening of examination, Dr. 

 Galle discovered the long-sought planet within one degree of the place predicted. 



Mr. Adams, of Cambridge, England, had discussed the same problem, and 

 had reached results very near those of Leverrier. The new planet was watched 

 by astronomers to determine if its elements agreed with the prediction. As it 

 moved extremely slow, this would have required a long series of years, but for 

 a remarkable discovery by Mr. S. C. Walker, at Washington, D. C. He 

 traced its orbit backward, and found the planet marked twice as a star in the 

 catalogue of Lelande, as far back as 1795, which gave sufficient data to com- 

 pute its entire orbit. . 



The mean distance of Neptune from the. Sun is 2,862,457,000 miles. The 

 eccentricity of its orbit is comparatively small, 49,940,000. It revolves 

 around the Sun in 60,126f days. Its orbi't is inclined to the ecliptic. 1 47'. < 

 Neptune is 31,000 miles "in diameter. A satellite has been discovered, and J 



