1889.] 



miJ Maij 1888 in fhe Doab and TioUmand. 



159 



of 7,000 or 8,000 feet ; and, knowing the vertical distribution of tempera- 

 ture, we can compute approximately the pressure at any given height. 

 The three stations of Roorkee, Dohra, and Mussooree lie within a hori- 

 zontal distance of little more than 20 miles, but their elevations above 

 sea-level are respectively 887, 2,233 and 6,881 feet. From observations 

 made at these places we may therefore determine the distribution of 

 temjierature almost exactly up to about 7,000 feet, and with some ap- 

 proach to accuracy for one or two thousand feet further. The computed 

 temperatures up to 10,000 feet for 10 a.m. and 4 p.m. each day, derived 

 from the observations of these throe stations, are the following : — 





29th April. 



30th April. 



lat May. 



2nd 



May. 



Height. 





































10 a.m. 



4 P. M. 



10 a.m. 



4 p. M. 



10 a.m. 



4 p. M. 



10 a.m. 



4 p. M. 



Sea-level 



100-2° 



1060° 



94 1." 



94-9° 



72-3° 



82-9'' 



90-5° 



95-0° 



1,000 Feet 



94' 2 



9S'4 



89-0 



92-7 



70 0 



82-3 



86-5 



91-4 



2,000 „ 



88 8 



91-5 



84-2 



89-8 



67-3 



80-5 



82-5 



87 3 



3,000 



84-0 



85-4 



80-0 



86-2 



64-2 



77-5 



78-5 



830 



4,000 „ 



79-8 



801 



76-4 



819 



60-6 



73-3 



74-5 



78-3 



5,000 



76-2 



75-4 



73-4 



76'8 



56-7 



67-9 



70' 5 



73-4 



6,000 „ 



73-2 



71-5 



71-0 



71-0 



52-3 



61-3 



66-5 



68-1 



7,000 „ 



70-8 



68-3 



69-2 



64-4 



47'5 



53-5 



62-5 



62-5 



8,000 „ 



690 



65-8 



68'0 



571 



42-3 



41-5 



58-5 



56-6 



9,000 „ 



67-8 



64-1 



67-4 



49-1 



36-6 



343 



54-5 



50-3 



10,000 „ 



67-2 



680 



67-4 



40-3 



30-6 



22-9 



50'5 



43-8 



The temperatures given in the last three lines are of course subject 

 to doubt, but up to 7,000 feet they may be accepted as correct. They 

 have been computed by the formula t = -\- dh -f hli^, the three constants 

 being determined by the observations of Roorkee, Dehra, and Mus- 

 sooree. 



On the 29th April, both at 10 A. M. and 4 p. m., the vertical distri- 

 bution of temperature was similar to the normal distribution in May, 

 given on page 152, that is to say, the decrease on ascending was at first 

 very rapid, but became less and less rapid as the height increased. 

 When the decrease is more rapid than 1° in. 183 feet, or 5'46° in 1,000 

 feet, the equilibrium of the atmosphere is unstable and convective 

 movements are almost certain to occur. Under ordinary circumstances, 

 as on the 29th Ajjril, these disturbances commence at the level of the 

 plain and probably bring about an interchange between the lowest layers 

 of the atmosphere and others at a considerable height,* such move- 



* To this interchange the liot west winds are probably dno, the feeble and 

 irregular currents ot the lower atmosphere being replaced during tlie hottest hours 

 ct the day by steady west winds descending from an upper layer. 

 21 



