THE SUN AND OTHER STARS 267 



The sun should be regarded as a largely gaseous mass, 

 which is in a state of wildest tumoil and confusion, with 

 terrific storms involving masses of matter hundreds or even 

 thousands of times as large as the earth some moving on 

 its surface with a speed of hundreds of miles a minute, others 

 shooting up from it with a speed exceeding a hundred miles 

 a second and ascending to heights of hundreds of thou- 

 sands of miles. This idea of the sun is very different from 

 that of the ancients, who imagined that the sun is a piece of 



FIG. 131. Explosions on the sun's surface 

 Photograph by the Yerkes Observatory 



burnished metal drawn across the sky by a chariot and horses 

 and that this little earth on which we live is the principal 

 object in the universe. 



271. Constitution of the sun. Although we are able to 

 measure the distance, dimensions, and mass of the sun, until 

 1860 it was supposed that we should never be able to find 

 out of what it is composed. The invention of an instrument 

 called the spectroscope opened a new world to us. Its opera- 

 tion depends upon the fact that when matter is in a gaseous 

 state the kind of light which it radiates depends upon the 

 composition of the radiating gas. For example, gaseous 

 hydrogen radiates certain kinds of light, gaseous oxygen 

 other kinds, and gaseous iron, copper, etc. still other kinds. 

 No two known substances in a gaseous state radiate exactly 

 the same kind of light, just as no two strings on the harp 

 give forth the same sound. 



