THE STARS. 161 



photographs were taken. The reduction of the 

 observations into the form of a catalogue was 

 spontaneously undertaken by the great Dutch 

 astronomer, Kapteyn, who was occupied with the 

 work for fourteen years, until in 1900 the great 

 catalogue, known as the ' Cape Photographic 

 Durchmusterung,' was completed. Half a million 

 stars are represented on the plates taken at the 

 Cape. 



By the time the ' Durchmusterung ' was com- 

 pleted, a greater undertaking was in progress. 

 Paul and Prosper Henry, astronomers at the 

 Paris Observatory, when engaged in continuing 

 Chacornac's ecliptic charts, applied photography 

 to their work, and found it very successful. 

 Accordingly Gill's proposal, on June 4, 1886, of 

 an International Congress of Astronomers, to 

 undertake a photographic survey of the heavens, 

 was enthusiastically received by the French 

 astronomers. The Congress met at Paris in 

 1887, under the presidentship of Amedee Mou- 

 chez (1821-1892), director of the Paris Observa- 

 tory, fifty -six astronomers of all nations being 

 present. The Congress resolved to construct a 

 Photographic Chart, and a Catalogue, the former 

 containing twenty million stars, the latter a 

 million and a quarter. Meetings were held in 

 Paris in 1891, 1893, 1896, and 1900 to super- 



L 



