AND ITS INHABITANTS 15 



tion of the other body. The line at a is longer than that at b 

 and the latter is longer than that at c. If N was not bound 

 together by its own gravity or rigidity, a, b, and c would 

 therefore drift apart and fan out while passing M. Consider 

 that rigidity is negligible, as in a fluid globe; then, if a minus 

 b, or b minus c are quantities which become greater than the 

 self-gravitative force of N holding together a and c, the unity 

 of the body becomes destroyed. The problem, however, is 

 not quite so simple, since the influence of all other points in 

 N must also be considered. 



As the nearer part of the body is pulled from the center, 

 and as the center is pulled from the farther side, there will, 

 further, be two simultaneous tides of approximately equal 

 height, but on opposite sides of the distorted body. They 

 tend to be always on the line joining the two bodies. Thus, on 

 the earth there are two tides on opposite sides, but the revolu- 

 tion of the earth on its axis, like a car wheel under two oppo- 

 site brake-shoes, gives an apparent effect, to one on the 

 surface of the earth, of a revolution of the tidal wave. As 

 a result of the equal tides at opposite ends of a diameter there 

 are, on any part of the ocean, two high tides in twenty-four 

 hours. 



Mode of tidal disruption in stars. A star is characterized 

 by its enormous size and mass and by the possession of a 

 gaseous constitution. The diameter and density are dependent 

 upon the balance at every point between the tremendous ex- 

 pansive forces of internal heat and the equally great compres- 

 sive forces due to its own gravity. If it contracts, then its 

 surface and each component shell below comes nearer to the 

 center, the effect of gravity upon any shell accordingly increases 

 inversely as the square of the new radius, and a higher internal 

 temperature becomes necessary to balance the higher gravita- 

 tive force. From this there results the paradox known as 

 Lane's law, that so long as a body maintains a gaseous 



