SOLAR DENSITY LOW. 



CH. XXVI11.] 



This brings us face to face with the density of this mass of 

 gas. Look at the first test. 



1. By the hypothesis the density of the sun must le low. 



We are accustomed, in dealing with the earth and comparing 

 it with other heavenly bodies, to refer to their density. We say, 

 for instance, that the density of the earth is five and a half 

 times greater than the density of water ; that is to say, that the 



403 



FIG. 120. Hypothetical section of the solar atmosphere. 



earth put in one scale-pan would weigh down five and a half 

 earths of the same size, if they were made of water, put in the 

 other. And we say, further, that the density of the earth is 

 about the same as the density of Venus and of Mars ; but the 

 density of the other planets is very much less. We know on 

 the earth that water as less dense, for instance, than mercury. We 

 know that spirit is less dense than water. All these represent 



D D 2 



