MIRACLES OF SCIENCE 



the structure of the sun is far less dense than that 

 of the earth, his substance having indeed only about 

 one and one-half times the density of water. This, 

 however, is quite what might be expected consider- 

 ing the revelations of the spectroscope as to the gas- 

 eous nature of such portions of the sun's surface as 

 can be explored. It is held, indeed, that the entire 

 substance of the sun may be regarded as gaseous, al- 

 though, owing to enormous gravitational compres- 

 sion, the main bulk of the sun's interior structure 

 doubtless has a consistency comparable rather to that 

 of a very dense liquid than to what we ordinarily 

 term a gas. 



But while the weighing of the sun seems thus 

 to be a very simple matter, it will be recalled that 

 we assumed at the outset a knowledge of the actual 

 distance that separates the earth from its primary, 

 and that this distance has an altogether vital share 

 in the calculation. But how is the sun's distance 

 itself to be determined? 



The question is a very vital one, not only in the 

 matter of estimating the sun's mass but in an endless 

 number of computations with reference to the dis- 

 tance and the bulk of the various members of the 

 solar system. The distance of the earth from the 

 sun is, indeed, a convenient yard-stick with which to 

 measure planetary distances. It is quite possible to 

 construct a plan showing the relative distances of 

 all the different planets from the sun, and to chart 

 with accuracy their orbits, without having any defi- 

 nite knowledge as to the actual distances involved in 

 any part of the chart. We could state with entire 



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