NO. 7 



THE ATMOSPHERE AND THE SUN — CLAYTON 



39 



two centers of negative departure. Fourth, these centers are not in 

 the same geographical position for the different periods and do not 

 remain fixed for successive epochs of the same period. The reasons 



Fig. 26. — 3.77-year period in pressure := i of 22.6 years. Departures at time 

 of maxima of solar period of same length. 



for these shifting centers are not clear. They are associated with 

 changes in the phase and ampHtude of the cycles. 



Changes in amplitude are both apparent and real. Apparent 

 changes occur where two periods of nearly the same length first 



Fig. 27. — 2.82-year period in pressure =:: i of 22.6 years. Departures at time 

 of maxima of solar period of same length. 



strengthen each other when they are in the same phase and then 

 weaken each other when they are opposed in phase. This change will 

 be familiar to most readers from diagrams to illustrate beats in sound 



