DISTURBING CAUSES. 49 



continually varying, both on account of the orbit 

 being an ellipse, on account of the different positions 

 of the moon, and other causes, yet these variations 

 are so small that, unless in so far as the atmosphere 

 and surface have temporary or local differences, the 

 general action of the sun may be regarded as at all 

 times the same, and the difference of seasons as re- 

 sulting entirely from the varying position of the illu- 

 minated hemisphere upon the globe. 



If the atmosphere and the surface were also uniform, 

 the heat and even the moisture and motion of the 

 atmosphere would be matters of easy calculation, and 

 the changes of the weather could be set down in the 

 almanac with as much certainty as the lengths of the 

 days, or the phases of the moon. The causes of va- 

 riation are, however, so many, some of them are so 

 difficult to be understood, and the result of the whole 

 is for very short periods so uncertain, that the natural 

 history of the weather, though one of the subjects 

 in which man is most deeply interested, is one in 

 which science has made comparatively little progress, 

 and upon which there still is consequently a great 

 deal of that superstitious credulity which is but too 

 apt to occupy those departments of nature where true 

 knowledge is deficient. Indeed, so hazardous is it 

 for even the best informed and the most cautious to 

 reason beyond the facts actually observed, with regard 

 to the temperature and succession of the weather, 

 that when trees were stated to come into leaf, roses 

 to blow, and the more hardy grains to ripen, in the 

 passes of the Himalaya mountains at a height of 

 more than 1600 feet above that which, from the exami- 



