Masterpieces of Science 



comet of that year appeared, it occurred to Dr. 

 Gill, the director of the observatory, that it 

 might be possible to photograph it. To the 

 telescope, pointed at the comet, a small camera 

 was accordingly attached. After a short ex- 

 posure the plate was developed and the image of 

 the comet came into view. So far as is known, 

 this was the first comet ever photographed. 

 The plate, moreover, showed not only the comet 

 which had been sought, but also stars which 

 were unsought, and that were quite invisible in 

 the telescope (Plate XVI). From their images, 

 thus unwittingly secured, came the project of a 

 new map of the heavens, which should reveal its 

 orbs to the limit of a plate's impressibility. 

 With the Observatory of ^Paris as their centre, 

 astronomers throughout the world are now en- 

 gaged upon a chart of the sky which will contain 

 at least twenty million stars. In future gener- 

 ations a comparison of the pictures now in hand 

 with pictures of later production will have pro- 

 found interest. Stellar changes ot place and 

 nebular alterations of form will indicate the laws 

 of the birth, the life, the death of worlds. 



At the close of the year 1899 there were stored 

 at Harvard Observatory 56,000 plates depicting 

 the heavens during every available night be- 

 ginning with 1886. Doublet lenses, of much 

 wider field than the single lenses usually em- 

 ployed, have been chosen by Professor E. C. 

 Pickering, the director, for this work. Thanks 

 to their use, certain of the plates have been found 

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