NO. 7 THK ATMOSPHERF. AND THE SUN CLAPTON 25 



averages. The letters a, b, c, etc., show successive maxima. The data 

 were derived from " World Weather Records " and cover the con- 

 tinent of Asia where the data are more complete for diiYerent lati- 

 tudes than in North America. 



It is seen from the plot that the maxima and minima of the period 

 occur first in high latitudes and successively later at stations nearer 

 the Equator, at least down to about 30° latitude, taking about three 

 years to move from Obdorsk, 66° N., 66° E., to Ley, 34° N., ']']'' E. 

 In the equatorial l)elt between 20° N. and 20° S. the maxima and 

 minima occur simultaneously at all stations as shown by the results for 

 Madras and Batavia. However, from figure 16 it is seen that the 

 pressures at Alma Ata, 43° N., and at Batavia, near the Equator, are 

 opposite in phase, which is further evidence that this wave traversed 

 90° of latitude in one period of about 3.75 years. 



A recent study of 2- and 3^-year waves in temperature by Ernest 

 Rietschel ' shows a rather complex movement indicating a combina- 

 tion of standing and moving waves. 



That the law of wave progress quoted above holds true in the 

 Southern Hemisphere as well as in the northern is shown by the 

 rate of progress of a temperature wave of about 18 days shown 

 plotted on page 223 of " World Weather." " This wave progressed 

 from Santa Cruz, 50° S., to Cuyaba, 16° S., in seven days, a rate 

 which would carry it from pole to Equator along a meridian in one 

 period of 18 days. 



The rate of progress of a 7.5-year wave is indicated in figure 22 

 where the maxima and minima of the waves occur successively later 

 at Stykkisholm, Rome, and Calcutta, the minima and maxima at 

 Calcutta being about 7 years later than at Stykkisholm. 



These facts render it evident that the rate of latitude displace- 

 ment is a general law for periodic oscillations of all lengths. This 

 law may be stated as follows : 



haw of hilihtde displacement of periodic zvaves. — Periodic oscil- 

 lations in atmospheric conditions progress in latitude from point to 

 point along a meridian at a rate that would carry the wave from 

 pole to Equator in one period, whatever the period of oscillation. 



It is probable that the law of displacement in longitude is equally 

 simple. Figure 14 shows that the 7-day wave progressed in longi- 

 tude alx)ut 180°, or half around the world, in seven days. 



^ Die 3-3^ jahrige und die 2 jahrige Tcinperaturschwankung, von Ernst 

 Rietschel. Geographical Institute of the University of Leipzig, Vol. IV, No. 1, 

 1929. 



