( 52 ) 



0.63 cos (lit — 64°.5) + 1.00 cos (2 nt — 290°) ') 

 As appears from Table I the phase shows small differences in the 

 different seasons, and at Batavia it is somewhat smaller than at the 

 three Dutch stations, but nowhere does it differ much from 300^, the 

 greatest height occurring everywhere about 10'* a. m. and. p.m. 

 According to a theory, tirst suggested by Kelvin, afterwards 

 mathematically founded by Margules, this regular variation can be 

 ascribed to a free oscillation of the atmosphere as a whole in its 

 own period of very nearly 12'', which again finds its origin in the 

 semi-diurnal term of the daily variation of the air temperature. 



Such an oscillation of the whole atmosi)here can be regarded as 

 a pressure wave, propagating from East towards West, witli a 

 velocity c of the heat wave and can be represented by the expression: 



p =z E cos l2}it — C -\ 



If, according to the observations -), we assume that 



E := Eg shi^ (p , 



then 



dp"\ dp SE cos (f 



— — cos {2nt — C) 



Ö?//;. — lid If R sin (p 



dp\ 2En 



— - j = -sin {2ut — C) 



OxJj=-Q c 



n 



c R sin (f 

 dp\ SE cos (f 



dyJx = o R sin (f 

 dp\ 2E 



and as 



cos {2nt -— C) 



, cos {Int - C — 90^). 



According to this theory therefore : 



A, — ;., = 270' 



and 



H, = V, H, cos <f . 

 For all i)laces situated in higher latitudes than 41° 49', therefore, 

 i/j y> //.,, and, according to (8) : 



«' — 0. 

 It ajjpears then that, at i)laces situated in latitudes higher than 



1) Observations. Vol. XXVIII (18C6-1905). p. 97. 



■~) Jaiürisgh. Zur Theorie der Luftschwankung. Meteor. Zeilschr. 24, 1907, p. 481, 



