EXPLORING THE GLORIES OF THE FIRMAMENT 



163 



Photograph from the Mount Wilson Observatory 



TERRIFIC EXPLOSIONS OX THE. SUN 



Think of eruptions so powerful that they hurl streams of gas farther from the sun than 

 the moon is from the earth, with a velocity frequently of a hundred miles a second and some- 

 times of two hundred. The}' leap up in great jets and flames, often changing their appearance 

 greatly in a quarter of an hour. The highest "prominence" here depicted reaches about ninety 

 thousand miles into space (see page 164). 



The spectroscope takes the visible rays 

 and their closest neighbors above and be- 

 low — the ultra-violet and the infra-red — 

 tears them into shreds, and assorts them 

 according to their wave-lengths with as 

 much certainty as a banker assorts the 

 different denominations of his money. 



It not only analyzes the light that comes 

 from the sun and the stars, but lights that 

 come from all the earthly elements. It 

 tells with equal fidelity whether a red par- 

 ticle is dried blood or colored paste, or 

 whether a rav of light came from iron or 

 from soda. It once revealed new lines 

 in an European mineral water. Forty 

 tons of the water had to be evaporated to 

 get two teaspoonfuls of the element, but 

 the spectroscope had detected its presence. 



In our childhood days we all recited 

 the stanza. "Twinkle, twinkle, little star": 

 but we no longer need to "wonder what 

 you are'' ; for now, as one authority tells 

 us, "Unto the midnight sky we the spec- 

 troscope apply." 



A photograph of the sun through some 

 of the more powerful spectroscopes shows 

 several million of the telltale lines. So- 

 dium has only two. calcium has seventy- 

 live, and iron has more than two thou- 

 sand. Thirty-nine of the common ele- 

 ments in the earth show lines that have 

 perfect matches in position, arrangement, 

 and character in the sun. 



HOW LIGHT IS TORX APART 



There are three classes of spectro- 

 scopes : In the one type the light is broken 

 up by being passed through prisms : in 

 the second class the light ray is torn apart 

 by the lines of a diffraction grating 

 through the same process that gives the 

 opal its color ; in the third kind the light 

 is separated by being passed through a 

 "stairsteps" of optical glass. 



The telescope lias proved that the same 

 laws of mathematics and mechanics that 

 govern the fall of an apple, the dropping 

 of a tear, or the rise of steam from a tea- 



