14 John Eliot — On the occasional Inversion of the Temperature [No. 1, 



This result is undoubtedly in part due to the greater length of 

 the night (or period of effective terrestrial radiation) than of the day 

 in the month of January in Northern India, and perhaps also to the 

 greater clearness and homogeneity of the atmosphere arising from the 

 stillness of the air and absence of wind at night as compared with the 

 day. It will, however, be presently seen it is probable that the mean 

 monthly minimum temperature at the hill stations represent an average 

 of conditions different from that at the plain stations and hence the figures 

 given above are almost certainly of little value for the comparison of 

 nocturnal radiation in the plains and hills of Northern India. It is, 

 however, evident that the figures as a whole support the inferences based 

 on the known laws of radiation from cooling bodies. It is certain there- 

 fore that in clear weather in January, if there were no other action than 

 mere radiation and heating and cooling of the adjacent air by contact 

 with the Earth's surface, the Earth's surface and adjacent air would be 

 heated to a greater extent by day and cooled to a larger amount at night 

 at the hill stations than at the plain stations and hence the daily range 

 of temperature might be expected on this account alone to be consider- 

 ably greater (probably from 10° to 20°) at the hill stations than at 

 the plains. 



The following table gives the average cloud amount during the 

 month at the selected stations. 







Mean proportion of cloud 



Ratio of cloud 







in January. 



proportion of hill 

 station to plain 



Names of pairs of stations. 







station. 







Hill 



Plain 









station. 



station. 



A. 







A. 



B. 



B. 



Quetta 



:::! 



4-4 



2-6 



1-7 



Jacobabad ... 









Murree 



:::} 



5-8 



4-4 



13 



Rawalpindi ... 









Simla 



:::) 



5-6 



39 



14 



Ludhiana 









Chakrata 



-\ 



4-8 



3-4 



1-4 



Roorkee 



... ) 









Ranikhet 



:::) 



41 



30 



14 



Bareilly 









Darjeeling ... 



:::} 



55 



1-7 



32 



Dhubri 









Mount Abu ... 



:::} 



2-6 



2-2 



12 



Deesa 









Pachmarhi ... 



:::} 



23 



2'2 



1-0 



Jubbulpore ... 









