ON THE SUN'S HEAT, 381 



of Sir Humphry Davy's " repulsive motion " 

 as suffices to keep it balanced as a fluid, without 

 either sinking or rising from the position in which 

 it was held by the thread of the screw. When 

 the matter is thus held up without the screw, 

 take away the screw or let it melt in its place. 

 We should thus have a pit from the sun's surface 

 to his centre, of a square metre area at the surface, 

 full of incandescent fluid, which we may suppose 

 to be of the actual ingredients of the solar sub- 

 stance. This fluid, having at the first instant 

 the temperature with which the paddle left it, 

 would for that instant continue radiating heat 

 just as it did when the paddle was kept moving ; 

 but it would quickly become much cooler at its 

 surface, and to a distance of a few metres down. 

 Currents of less hot fluid tumbling down, and 

 hotter fluid coming up from below, in irregular 

 whirls, would carry the cooled fluid down from the 

 surface, and bring up hotter fluid from below, but 

 this mixing could not go on through a depth of 

 very many metres to a sufficient degree to keep 

 up anything approaching to the high temperature 



