ATM 



tion must be applied thus: Let h = height found by the above rule, 

 then 



- correction to he subtracted from //. 



48600 



According to Atkinson (see Mem. Astrox. Hoc.) the height in feet due 

 to any given depression of the thermometer w, i.s 



and n 



nearly. 



which two formulae apply to both hemispheres. 



20. To find the mean temperature of any day, under any parallel, and 

 with any elevation. 



Let A. be the mean longitude of the sun, computed from the 1st of arica 

 for any day of the year, the mean temperature of which is y ; then in 

 these latitudes. 



y = 58<> + 370 cos 2 lat. - -^L + 150 x sin (A - 30") 



21. On ascending into the atmosphere, there is a certain height in every 

 latitude, where the mean temperature is below 32 ; the curve joining all 

 these points, is called the line of perpetual congelation j to find its height 

 in any latitude. 



H 7642 -f 7933. cos. 2 L. (Play fair.) 



TABLE of the height of the curve of congelation in different latitudes^ 

 as computed by Leslie. 



Lat. 



00 



5 . 

 10, 

 15 . 



25 



30 

 35 

 40 

 45 

 50 

 51 

 52 



Ht. of curve in feet. 

 _, ,_ 15207 



~~~^~~ 15095 



_ 14761 



11220 

 13478 

 12557 

 11484 

 10287 

 9001 

 76* J 

 6334 

 6070 

 5808 

 5548 



