CHARTING THE UNIVERSE 



geometrical ratio with each decrease of magnitude. 

 A one-inch glass shows stars of about the ninth mag- 

 nitude, to the number of more than a million and a 

 quarter. A three-inch glass opens up vistas that in- 

 clude twelfth magnitude stars. The twenty-five-inch 

 lens shows sixteenth magnitude stars to the number 

 of at least one hundred million; the forty-inch Yerkes 

 lens brings to view yet remoter galaxies; and the five 

 foot Mt. Wilson reflector records on the photo- 

 graphic plate, in myriads beyond all computing, stars 

 estimated by Professor Pickering at the twentieth 

 magnitude. 



Newcomb computes that the telescope reveals 

 stars 10,000 times fainter than the faintest to be seen 

 with the naked eye. Ball tells us that the modern 

 telescope "separates" double stars that are so near 

 together that to see them double is equivalent to 

 separating two candles less than two inches apart at 

 a distance of forty miles. 



THE WONDER-WORKING SPECTROSCOPE 



And where the telescope fails us, the spectroscope 

 takes up the work of extending the limits of the visi- 

 ble. This instrument, which consists essentially of 

 a prism or a finely ruled grating which splits up a 

 beam of white light into the primary colors, analyzes 

 the light of distant stars (except the very most dis- 

 tant which are too faint with present telescopic 

 powers) as readily as it analyzes the light of a hydro- 

 gen flame in the laboratory. It serves also to reveal 

 any movement of a star in the line of sight. If the 

 star is coming toward us the light waves are, as it 



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