262 MR. J. BAXENDELL ON PERIODIC DISTURBANCES 



by the union of the first maximum of one year with the 

 second maximum of the year preceding, the interval be- 

 tween the two maxima being twelve months. It is evident, 

 therefore, that these maxima move across the two conti- 

 nents in opposite directions, the course of the first being 

 from west to east, and that of the second from east to 

 west. 



If these two maxima were produced by independent 

 causes it might be expected that their joint action in the 

 mouth of January would produce a compound maximum 

 of much greater elevation than either of the separate 

 maxima ; but as this is not the case it appears to me very 

 probable that both maxima are produced by the same dis- 

 turbing cause, such disturbing cause taking its rise in 

 Eastern Asia in the month of November, and gradually 

 moving westward until it arrives in the British Islands in 

 January ; then, reversing its course, it returns with a 

 diminished velocity to the region of its origin, where it 

 arrives in the month of April, and afterwards rapidly dis- 

 appears under the influence of an increasing temperature, 

 to appear again later in the year on the return of a low 

 temperature. 



The middle latitude of the area over which these peri- 

 odical disturbances of atmospheric pressure take place is 

 about 51°, and the difference of longitude of the extreme 

 east and west stations being about 126°, it follows that the 

 length of this area is more than four thousand six hundred 

 geographical miles ; and as tliQ diff'erence of latitude be- 

 tween the extreme north and south stations in Eastern 

 Europe and Western Asia is more than 19°, its breadth 

 must considerably exceed eleven hundred miles. 



With reference to the probable nature and origin of the 

 disturbing cause it may be remarked that the times of its 

 first appearance and final disappearance in Eastern and 

 Central Asia correspond very nearly with the times of the 



