or. xxxiv. CELESTIAL PHOTOGRAPHY. 347 



and then to observe how far the star lines differ from exact 

 coincidence with the lines of the incandescent gas. Dr. 

 Huggins established by this means the fact that Sirius is 

 moving away from our earth at the rate of about 25 miles 

 a second, after allowing for the motion of our own solar 

 system through space. This method has now been applied 

 to a large number of stars, not only by Huggins and others, 

 but also on a large scale at the Greenwich Observatory. 



Celestial Photography. While all these wonderful 

 results have been obtained by the spectroscope, photography 

 has been advancing so rapidly that the very mountains and 

 valleys in distant planets, and the impressions of the still 

 more distant stars, and of fleeting comets, are now brought 

 under our eyes in photographs. In 1864 Mr. Rutherford 

 produced his magnificent photographs of the moon, and of 

 star-groups, especially the Pleiades. In 1880 Professor 

 Draper of America photographed the nebula of Orion. 

 In 1885 the brothers Henry of Paris took photographs not 

 only of the remotest planets, but even of the Satellites of 

 Neptune and Saturn, the last of which is so faint that it 

 can only be seen with the most powerful telescope. Nor 

 is this all, for they actually discovered by photography a 

 nebula surrounding the star Maia of the Pleiades, which 

 till then was quite unknown. Encouraged by such great 

 success, astronomers now propose to photograph the whole 

 of the heavens; and on April 18, 1887, a memorable 

 International Congress took place in Paris, at which it was 

 agreed to carry on the work at selected stations all over the 

 world. Not only in Europe, the United States, and 

 Australia, but in Mexico, Brazil, Chili, the Argentine 

 republic, and numerous other countries, preparations are 

 being made, and when the work is completed it is estimated 

 that there will be 11,000 plates covering 2000 square 



