NO. 7 THE ATMOSPHERE AND THE SUN CLAYTON 21 



the averages ; sine curves computed from the data by harmonic analy- 

 sis are shown by clotted lines. Here, again, it is fovmd that the 

 maxima and minima of the oscillations occur later at the more south- 

 ern stations and the phase is inverted at St. Paul, showing that the 

 progressive movement is only about one half as rapid as the 7-day 

 period. In other words the ratio, rate of progress divided by length 

 of period, is the same for both periods and apparently for all periods, 

 as will be shown later. 



That atmospheric pressure and temperature may be analysed into 

 waves or oscillations which move at different speeds inversely pro- 

 portional to their wave length was advanced by me in the monthly 

 Weather Review, April, 1907, and has been confirmed by a num- 

 ber of research workers, Defant, Vercelli, Danilow,' Clough,^ Weick- 

 mann,^ and others. These waves do not always move from the same 

 direction, as Danilow and Weickmann have pointed out ; but the 

 dominant direction of motion is from northwest to southeast in the 

 northern hemisphere and from southwest to northeast in the south- 

 ern hemisphere.'' 



The rate of progress for all classes of moving atmospheric waves 

 appears to follow a very simple law. This may be illustrated by the 

 progress of the 7-day wave. Using the data from about 16 sta- 

 tions, the progress of the wave from Alaska is illustrated in figure 14 

 by a series of heavy lines giving the wave front on successive days 

 as it passed across the North American Continent. Small circles show 

 the positions of the stations used. It is seen that the wave moved 

 from about 180° W. longitude at a rate which would carry it half 

 around the world in one period of oscillation, namely in seven days, 

 and hence entirely around in two periods. At the same time the 

 wave front advanced from the Arctic Circle near Nome to the Tropic 

 of Cancer near Key West also in a period of seven days or at a rate 

 which would carry it, from pole to Equator in the time of two periods 

 of oscillation. 



If, however, the rate of progress is taken not along the wave 

 front but along a meridian — in this case the 90th meridian west is a 

 good example — the rate of progress southward from the Arctic 

 Circle to the Tropic of Cancer takes place in 3^ days, or at a rate 



' Wetterwellen, Podoleschen Abtheilung des Ukrainischen Meteorologiches 

 Dientes, 1926. 



^ Monthly Weather Review, Vol. 52, No. 9, p. 436, Sept. 1924. 



' Weickmann, L., Das Wellenproblem der Atmosphiire. Meteor. Zeitschr., 

 S. 241, 1927. 



* Clayton, H. H., World Weather, p. in. New York, Macmillan & Co., 1923. 



