1890.] Relations between the Hills and Plains of Northern India. 4)7 



considerable elevations above the plains is nearly constant, 

 and is determined by the temperature at that elevation of 

 the rapid upward convective currents at the hottest period 

 of the day. 



(6) — There is at such periods a slow steady descent of air during the 

 night from the hills towards the plains and a horizontal in- 

 flow from higher levels of air at nearly constant tempera- 

 ture to the hills. 



(c) — Temperature decreases very rapidly at the hill stations shortly 

 before and for some little time after sunset until the tem- 

 perature falls to or slightly below that of the same level in 

 the open atmosphere over the plains of Northern India, after 

 which it remains nearly constant throughout the night. 

 The short chilly period immediately after sunset is a 

 very characteristic feature of the hill stations in ordinary 

 fine weather during November, December, and January. 



(d.) — The temperature of the earth's surface in the plains of Nor- 

 thern India falls rapidly and steadily during the whole night 

 and until very shortly before sunrise. Hence also the 

 temperature of the quiescent mass of air immediately above 

 it falls pari passu, and by amounts ranging from .30° to 

 40° in ordinary clear weather in January. The fall of 

 temperature is greatest at a considerable distance from the 

 foot of the hills, where the observations shew that the 

 maximum temperatures are higher, the daily range of tem- 

 perature greater, and the minimum frequently lower than 

 immediately under the hills The following gives examples 

 for the 2nd and 3rd January, 1889. The stations which were 

 to be compared are grouped by means of brackets. 



Station. 



2nd 



3rd 



Max. 



Min. 



Range. 



Max. 



Min. 



Range. 



Lndliiana ... ... ) 



Lahore ... ... j 



697 



410 



28-7 



75-2 



45-6 



29-6 



72-0 



36-2 



358 



730 



372 



358 



Koorkee ... ... \ 



708 



38-9 



319 



70-8 



36 6 



34-2 



Meerut ... ... \ 



72-7 



42-1 



30-6 



74-2 



390 



35-2 



Delhi ) 



731 



411 



320 



78-1 



401 



380 



Bareilly ... ... j 



Agra ... ... .1 



73-7 



41-3 



32-4 



712 



398 



31-4 



75-6 



44-6 



310 



78-6 



43-6 



350 



Gorakhpnr ... .. "^ 



68-9 



454 



23-5 



71-8 



47-9 



23-9 



Lucknow ... ... ? 



75-2 



43-0 



32-2 



711 



411 



300 



Allahabad ) 



71-4 



43-7 



27-7 



770 



427 



343 



