48 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



mean a revolution in present methods of weather forecasting. The 

 forecasting of pressure and temperature will be made in much the 

 same way that ocean tides are now predicted, except that the periods 

 used will be solar periods rather than lunar periods and will need 

 to be treated in a special way owing to changes in phase and 

 amplitude. 



Such a successful forecast as that shown in figure 31 seems con- 

 clusive evidence that day to day weather is not a haphazard occur- 

 rence as many persons believe, but is subject to calculation. It is 

 evident that changes of pressure are calculable to some extent now, 

 and the calculations will, no doubt, in the future be made with 

 increasing accuracy for weeks and perhaps months in advance. Proc- 

 esses will be simplified and machinery like the tidal machines will be 

 introduced in order to handle the immense amount of data which will 

 be needed for world-wide forecasts, or even for forecasts over a large 

 area like the United States. 



SUMMARY 



This paper contains evidence pointing to the following conclusions : 

 Solar activity varies in complicated pulses. These pulses or varia- 

 tions in intensity are attended by variations of pressure in the earth's 

 atmosphere. When solar activity, as indicated by spots and radia- 

 tion values, increases, the latitude contrasts of pressure in the earth's 

 atmosphere are increased and atmospheric circulation speeded up. 

 The pressure falls in the equatorial belt, rises in middle latitudes 

 and falls in the polar regions. When solar activity decreases the 

 reverse conditions occur. The zonal regularity of these changes is 

 interfered with by the distribution of land and water and by seasonal 

 changes. 



Immediately following the decrease of pressure in the polar region 

 with increased solar activity, a wave of decreased pressure moves 

 toward the Equator. With decreased solar activity the pressure in 

 polar latitudes increases and a wave of increased pressure travels 

 towards the Equator. These waves move with a speed proportional to 

 the length of the solar pulse or period causing them. If the period of 

 oscillation is seven days the wave moves from pole to Equator, when 

 measured along a meridian, in seven days. If the length of the 

 oscillation is 2"/ months, or 2\ years, the time of the wave movement 

 from pole to Equator is 27 months and if the length of the period is 

 7^ years the time of movement from pole to Equator is 7^ years, or 

 one period of oscillation in each case. 



