1890.] Relations betiveen the Hills and Plains of Northern India. 



13 



This table establishes conclusively that the average direct heating 

 power of the sun is greater at the hill stations in January than at the 

 corresponding plain stations. And, if it might be assumed that the re- 

 lative intensity in the two cases is, roughly speaking, proportional to 

 the ratios given in the preceding table, the heating power of the sun at 

 an elevation of 7000 feet in the Himalayas is on the average about one- 

 fifth greater than at the level of the adjacent plains, or, in consequence of 

 the absorbing action of the lower strata, the sun is one-sixth less power- 

 ful in heating the earth's surface at the level of the plains than it is at 

 that of the hill stations of the Himalayas. 



The following table gives similar data for nocturnal radiation from 

 the Earth's surface : — 



Names of pairs of stations. 



Average difference between 

 grass radiation thermo- 

 meter readings and those 

 of minimum in shade ther- 

 mometer for January. 



Ratio of differ- 

 ence for hill 

 station to that 

 of corresponding 





Hill 



station. 

 A. 



Plain 



station. 



B. 



plain station 

 A. 

 B. 



Quetta ... ... ... ) 



Jaoobabad ... ... ... ) 



Murree ... ... ... 1 



Rawalpindi ... ... ... ) 



Simla ... ... ... S 



Ludhiana ... ... ... j 



Chakrata ... ... ... S 



Roorkee ... ... ... j 



Ranikhet ... ... ,.\ 



Bareilly ... ... ... J 



Darjeeling ... ... ... l 



Dhubri ... ... ... \ 



Mount Abu ... ... ... i 



Deesa ... ... ... | 



Pachmarhi ... ... ... "i 



Hoshangabad ... ... j 



10-4° 

 11-4° 

 122° 

 9-5° 

 13'0° 

 10-3° 

 17-1° 

 120° 



10-1° 

 7-3° 

 9-8° 

 7-2° 

 8-3° 

 69° 

 9-1° 

 8-5° 



1-0° 

 1-6° 

 1-3° 

 1-3° 

 1-6° 

 1-5° 

 19° 

 1-4° 



These figures show that nocturnal radiation goes on much more 

 rapidly at the hill stations than at the adjacent plain stations, and that 

 the ratios as measured by the differences given in the preceding table are 

 much greater than the ratios in the corresponding tables for solar radia- 

 tion. Taking the average of all the stations as a rough approximation, 

 they appear to indicate that nocturnal radiation goes on upwards of 50 

 per cent, more rapidly at the hill stations than at the adjacent plain 

 stations. 



