CIRCULATION OF THE ATMOSPHERE 457 



tion of velocity falls off gradually towards the poles, until at the poles 

 it takes something like 30 days to turn around. There is evidence to 

 show that in the polar zones or near the poles there are certain variable 

 velocities of rotation. These may belong to different sections in the 

 sun's atmosphere. Our observations at the poles cut through the sun's 

 atmosphere, as it were, parallel to the surface. At the equator our 

 observations look down vertically through the sun's atmosphere. We 

 can therefore near the poles get the same kind of observations at dif- 

 ferent solar levels. However this may be, the turbulence of motion 

 seems to be much greater near the poles than near the equator. Within 

 the sun's mass we can well imagine that many different periods of 

 rotation, or of the daily angular velocity, actually exist. Looking at 

 the solar surface as a unit, it consists of a huge wave whose crest ad- 

 vances around the equatorial regions at a considerably greater speed 

 than in the polar regions. Now our mathematical analysis indicates 

 that such a circulation can be maintained if the solar temperatures are 

 greater in the polar regions than in the equatorial regions. That is a 

 form of vortex, applicable to the solar mass, in which the velocities 

 and temperatures are so connected together that the polar regions are 

 warmer and have a slower angular velocity than the equatorial regions 

 which are cooler with a greater angular velocity. This, therefore, is 

 a condition of affairs practically the inverse of what we have been de- 

 scribing in the atmosphere of the earth. It is of course in some way 

 associated with the great heat cauldron which is boiling inside the 

 solar surface, where the heat accumulates and congests and finally 

 works its way to the surface by means of this gigantic solar vortex. 

 Within the great vortex there are innumerable minor vortices. These 

 vortical tubes generally stretch from north to south perpendicular to 

 the plane of the equator. These vortex tubes may be very irregular 

 and broken up, but as a whole the sun may be described as a polarized 

 mass throughout which the minor motions are nearly parallel to the 

 plane of the equator. 



Solar Phenomena 



The different levels in the sun's atmosphere have received the fol- 

 lowing names : The lowest one which is visible is called the photo- 

 sphere, and consists of mottled shapes like cumulus cloud forms, 

 bright and dark areas being interspersed. Above this is the chromo- 

 sphere, a layer of hydrogen and calcium and other gases 5,000 or 6,000 

 miles thick. The lower surface of the chromosphere is a reversing 

 layer, so called, and is the level at which the dark lines of the solar 

 spectrum are formed. Through these layers are projected jets of hydro- 

 gen and calcium flames which stretch out beyond the visible edge of the 

 sun called prominences, and far beyond the region of the prominences 



