MASTEE KEY OF SCIENCE RUSSELL 135 



plates have been developed which are sensitive to the red end of the 

 spectrum, and liowland had no such plates available. Partly for 

 that reason, and partly because some substances are now available 

 of which Rowland could not get specimens, 60 chemical elements 

 have now been identified in the sun — most of them with certainty. 



In the stars, we can not observe such immense detail as we can in 

 the sun, although the big spectroscopes that are now being attached 

 to the great refractors such as the Mount Wilson 100-inch telescope 

 give us an amazing amount of information, and dozens of different 

 chemical elements have been definitely identified in the stars. 



The minute shift in the position of the lines due to motions of 

 approach or recession has enabled us to detect and measure the rota- 

 tion of the sun and the planets, to prove that Saturn's rings are not 

 solid, but composed of myriads of tiny satellites, and to get one of 

 the most accurate determinations of the sun's distance. Applied to 

 the stars, it has determined the sun's motion among them, the dis- 

 tances of hundreds of individual stars, and the average for thou- 

 sands more ; has revealed hundreds of double stars too close to be 

 resolved by the telescope, and determined the masses and even the 

 diameters of some of them ; and has disclosed those amazingly rapid 

 motions of the remote nebulae — some as high as 15,000 miles a sec- 

 ond — which point the Avay to new conceptions of the nature, the past, 

 and the future of the material universe. Spectroscopic tests have 

 shown that the nebulae are of two kinds, one consisting of masses of 

 luminous gas; the others, giving light like stars, must themselves be 

 great clusters of stars at gigantic distances. 



If the spectroscope has thus proved so profitable to the astronomer, 

 what has it accomplished for scientists in other fields ? The chemist 

 owes to spectroscopy the discovery of at least 10 of the elements, 

 some by optical methods, others more recently by the aid of X rays. 

 Among these is helium, which was detected in the sun and its nature 

 as a light gas correctly interpreted more than 20 years before it was 

 '■' run to earth." 



The classical physicist finds in the spectroscopic data his most 

 precise standards of length, and some of his more accurate methods 

 of measurement. My friend, Doctor Meggers, of the Bureau of 

 Standards, and his associates have developed very practical spectro- 

 scopy recently. Suppose, for example, you have some fusible plugs 

 that are used in our overhead sprinkler systems. They are made 

 of a fusible alloy which will be greatly damaged if it has any more 

 than the most minute quantity of iron in it. To find this out by 

 chemical analysis is a slow and tedious process; but you can take 

 one of these plugs and test it with the spectroscope, and if the strong 

 lines of iron show up, you know there is iron there. Comparative 



