18 Chacornac' s Solar Theories. 



tion of the incandescent matter is accompanied by explosive 

 emissions of gas.* 



To account for the appearance of spots, exceptionally, in the 

 equatorial regions, M. Chacornac remarks that evapora- 

 tion is most rapid when the atmosphere in which it takes 

 place is least dense, and that the quicker it takes place the 

 greater the local loss of heat. At the sun's equator, gravity 

 being less than at any part of his surface, the pressure of his 

 atmosphere is less than at the poles, and thus phenomena like 

 our trade-winds must arise. Evaporation would be very rapid 

 at the equator, and the rarefaction of the atmosphere would 

 favour radiation. " If the liquid,' incandescent surface cools 

 itself more rapidly at the equator than in other zones, it must 

 give rise to currents, as the difference of temperature in our 

 seas between surface and depths occasions superficial and deep 

 currents in opposite directions. If the cooled layers have a 

 tendency to descend into the interior mass, the adjacent layers 

 make a descending rush to fill up the void. This then is a 

 superficial current, teuding to carry matter from the poles to 

 the equator. We mark also that this current transports fluid 

 masses animated with a movement of rotation less rapid than 

 that of the zones which they enter, and in virtue of this 

 retardation, they seem to lag behind when compared with the 

 fluid masses moving in zones of less latitude.'" 



The currents resembling our trade-winds acting in a direction 

 opposite to the accelerated movement of the external mass — 

 for at the equator vapours rise more rapidly than at the poles — 

 it results, from the combination of these opposite currents, that 

 the central mass appears to have a movement of rotation more 

 rapid than that of his photosphere. This difference of move- 

 ment occasions the particular arrangement of spots, and the 

 formation of groups elongated in a direction often parallel. 



Eeferring to the " magnificent work of Mr. Carington," 

 showing, amongst other things, that the velocity of rotation of 

 solar spots is a function of latitude, M. Chacornac remarks 

 that it will be interesting to ascertain if a variation in the 

 phenomenon of evaporation occasions deviations from this 

 law. 



In 1857, M. Chacornac states that he remarked a coinci- 

 dence between the period of a revolution of Jupiter and two 

 consecutive returns to a minimum of solar spots, as noticed by 

 M. Schwabe, of Dessau, and he conceived a connection between 

 the minima of the radii vectories of Jupiter and those of the 



* M. Chacornac mates frequent reference to the theories of " surfusion and 

 dissociation," by which M. Fouruet and others have explained certain appearances 

 in terrestrial geology, but we have not thought it necessary to cite these passages 

 in detail. 



