48 F. W. Very— A Cosmic Cycle. 



able to follow the demands put upon it for the disposal of 

 thermal energy produced by contraction. Our sun has already 

 reached the stage where viscosity is sufficient to cause the 

 retention of abnormal distributions of heat in particular locali- 

 ties, since spots frequently recur in the vicinity of the same 

 heliographic latitude and longitude. 



There is a third mode by which internal energy may be 

 brought to the surface, namely, by some explosive force of 

 sufficient power to overcome the enormous resistance of pres- 

 sure. Such a force is witnessed in the production of explosive 

 solar prominences whose angles of divergence prove that their 

 point of origin is at a considerable depth. Cases of simultane- 

 ous spots or prominences on opposite sides of the sun are 

 known. Here it is possible that an originating explosion at 

 the very center of the son has started a commotion powerful 

 enough to reach the surface. At the center the pressure is 

 presumably greatest. If this pressure is for any reason a criti- 

 cal one, limiting a condition ot unstable equilibrium, a sudden 

 increase or decrease of pressure may precipitate an explosion. 

 Such an unstable condition exists when water in the spheroidal 

 state remains suspended over red-hot metal. Sudden lowering 

 of pressure, obliterating the intermediate layer of steam, pro- 

 duces complete contact of water and metal, and starts an ex- 

 plosion. 



Within the sun, I shall assume that increase of pressure, due 

 to contraction, accumulates from time to time until it surpasses a 

 certain critical point, depending upon some condition of the 

 mass which remains to be determined, and that explosion 

 occurs (or a series of explosions), restoring equilibrium tempo- 

 rarily. 



Since centrifugal force diminishes gravitational pressure as 

 the equator is approached, ascensional motions produced by 

 central explosions can more easily reach the surface near the 

 equator. In this way a surface layer of relatively hot material 

 will tend to accumulate in a broad equatorial zone, and where 

 the horizontal surface temperature-gradient is steepest, let us 

 suppose somewhat nearer the equator than midlatitude, convec- 

 tional storms begin, gradually approaching the equator as the 

 disturbing layer of hot material is used up. Increasing radia- 

 tion during the stormy period produces more rapid contraction 

 and restores the central critical pressure. The solar spots 

 being local phenomena may be influenced by various subordi- 

 nate causes, such as the fall of meteoritic matter on certain 

 regions of the solar surface, and minor irregularities of spot- 

 sequence may be produced in this way ; but the general sun- 

 spot period, being due to the deep-seated circulation, should 

 exhibit a constancy and stability proportionate to the magni- 



