24 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



Memphis, Vicksburg and New Orleans have been derived and it is 

 found that there is an average lag of 0.19 year from St. Paul to 

 St. Louis and a lag of 0.37 year between St. Paul and New Orleans." 

 The distance from St. Paul to New Orleans is 15° of latitude and 

 0.37 year is about one-sixth of the period, so that the rate of prog- 



Fig. 1 6. — Pressure in 3.77-year period. 



ress here indicated would carry the wave from pole to Equator in 

 one period. 



In figure i6 is found a period in which the unit of time is years 

 instead of days. The period of oscillation in i)ressure is about four 

 years. It was taken to be 3.75 years, or one-third of a sun-spot 

 period of 11.3 years, and averages were made for each three suc- 

 cessive oscillations of 3.75 years. The continuous curves show the 



