Photography of the Skies 



other which permits only light of a single colour 

 to reach his photographic plate. Because this 

 light is of but one hue, pictures can be obtained 

 of objects not to be photographed in any other 

 way. Moving the apparatus at will, he secures 

 photographs of the prominences around the 

 edge of the sun, as well as of the whole surface 

 of its disc. A visual examination of the promi- 

 nences would require two hours, but pictures of 

 them may be taken in two minutes. Many 

 faculae [bright spots], undiscernible by any 

 other means, have been brought to view by Pro- 

 fessor Hale's instrument, which he calls the 

 spectro-heliograph. The device was suggested 

 by Janssen as long ago as 1869; it was inde- 

 pendently invented by Professor Hale in 

 1889. 



The extension of disclosures by the camera in 

 regions blank to the eye seems without bound. 

 Beyond the violet ray of the solar spectrum ex- 

 tend vibrations which, though invisible, have 

 been caught on photographic plates ever since 

 the experiments of Scheele in 1777. Victorium, 

 an element recently discovered by Sir William 

 Crookes, has a spectrum high up in the ultra- 

 violet region, which, therefore, can be studied 

 only photographically. More than one element 

 has made its first appearance to the chemist as 

 he has observed the spectrum of the sun. Helium 

 thus introduced itself long before its discovery in 

 the atmosphere of the earth. Coronium, which 

 appears in the solar corona, has been diligently 

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