486 T. C. CHAMBERLIN 



It is a notable fact that the equatorial belts of the sun, Jupiter, 

 and Saturn rotate faster than portions of their surfaces on the same 

 meridian in higher latitudes. This has been the subject of much 

 speculation and has received different explanations, more than one 

 of which may contain a measure of truth. One suggestion is that 

 it is due to the infall of planetesimal matter. A closely allied 

 suggestion is that it is due to the falling back of matter ejected 

 from the sun into the planetary regions and drawn forward in the 

 direction of their motion, so that on returning it carries surplus 

 momentum acquired from the planets. These are not inconsistent 

 with the suggestion here made that part of the acceleration may be 

 merely a phase of circulation normally set up in such hot rotating 

 gaseous bodies. In a hot fluid body of the volume and rate of 

 rotation of the earth, a mass, cooling and sinking from the equa- 

 torial surface, would — if it were free from contacts with surround- 

 ing matter — acquire an orbital velocity before it reached the 

 center, and hence would sink no farther because the centrifugal 

 component of its motion would wholly offset the pull of gravity 

 upon it. If forced below that depth, its centrifugal component 

 would act as a buoyant force. Of course, the sinking mass never 

 would be free from contacts, and so it would necessarily exchange 

 energies with the contact matter. The sinking mass would thus 

 act as an accelerating undertow for any matter that flowed in above 

 it as it sank; so also it would tend to drag forward whatever was 

 in contact with it on its sides and below. It is not difficult to work 

 out a system of circulation actuated by such equatorial cooling and 

 sinking. It would, however, undoubtedly be subordinate to the inti- 

 mate turbulence that would spring from other factors. The axial 

 tract would present a unique problem, for it would be little affected 

 by rotation and would not directly be reached by the descending 

 equatorial currents, for they would be restrained by the centrifugal 

 component of rotation and turned northward and southward, 

 completing their circuits by return from the higher latitudes with 

 such deflections as rotation imposed. This part of the circulation 

 may be pictured as two vortex rings made up of spiral submove- 

 ments trending downward on their contact sides at the equator and 

 upward on their poleward sides. The axial tracts in themselves 



