INTRODUCTORY ESSAY. 83 



earth) is usually estimated at one degree for three hundred 

 feet. lu India, it is only in the most perennially humid and 

 densely wooded mountains, that the diminution of tempera- 

 ture is so rapid as this, for in the drier districts it is very 

 much less. Thus, while in Sikkim 1° for 300 feet is the pro- 

 portion for elevations below 7000 feet, on the Nilghiri Hills it 

 is about 1° for 340 feet, in Khasia 1° for 380 feet ; and the 

 elevations of Nagpur and Ambala produce no perceptible di- 

 minution in their mean temperature, which is as great as 

 that which would normally be assigned to them were they at 

 the level of the sea. 



When the latitude, the amount of land, the humidity, and 

 the elevation are known, we have every element which influ- 

 ences climate; and as the limits between which each of these 

 elements varies is in India considerable, it is evident that 

 the diversity in the climate of its parts must be very great. 

 We reserve the details of these to the following chaptei", and 

 shall confine ourselves here to pointing out the two broad 

 divisions of climates, which it is important to bear in mind, 

 namely, those which are excessive, and those which are equable. 



An equable climate prevails in the vicinity of the equator, 

 and in all perennially humid districts ; while an excessive cli- 

 mate, in which the summer is very hot and the winter cold, 

 is characteristic of the north-western regions, of the interior 

 of the continent, and of provinces characterized by extreme 

 drought. The northern districts of India are more exces- 

 sive in climate than the southern, because they are broader 

 expanses of land ; and the western side of the great (Madras) 

 peninsula is more equable than the eastern, because it is much 

 more humid. 



VI. Sketch of the Physical Features and Vegetation of t/ie 

 Provinces of India. 



A. Limits of the 'Flora Indica.' 



Although the main object of this Flora is the illustration 



