MOVEMENTS OF ATMOSPHERE — -GULDBERG AND MOHN 229 



Let a c be the direction of the thermometric gradient /, and draw 

 b c perpendicular to a c: the temperature is the same at b and at c 



and the increase of temperature from a to b is / — . Introducing 





 a c = d s cos y and the value of i° we have 



9 



d t = — / cos yds 

 10 6 



Denoting the variation of the temperature per hour by i, we have 



i = 3600 — 

 dt 



Since 



u= ds , 



dt 

 we find 



* = 0.0324 J U cos y 



The angle y depends on the angle y between the thermometry 

 gradient and the axis, and we have 



y = <p + (j> + y 



Consequently we shall find 



* = 0.0324 J U cos (<p + 4> - y) (3) 



By the aid of this equation we can construct curves of equal varia- 

 tion of temperature. Supposing y to be constant we shall have for 

 i = o, 



<p=-~ — (p+y = constant. 



Hence, the curve of no variation is a straight line which passes 

 through the center of the cyclone. 



It is evident that there exists some relation between the velocity 

 of propagation W and the thermometric gradient J. According 

 to equation (6) of §31 we have 



W = 2.78~°cos o Tl ~ T2 

 £0 r o 



