':346 Professor Arthur ScJtuster [^I^iy 1^» 



staff of thirteen workers under him. There are in addition nineteen 

 experts or referees representing the different sciences. The annual 

 office expenses, inchiding salaries, amount to about 22U0/. ; while the 

 expenditure on printing, ])inding and publication in the year ending 

 March 1, 11)05, amounted to nearly 41)00/. The two items are just 

 covered by the guarantees of the different countries which, as already 

 mentioned, take the form of subscriptions for copies of the catalogue, 

 so that it may be said that the Central Office is self-supporting. 

 After so short a time of working, this success must be a source of 

 considerable satisfaction to Professor Armstrong and those who have 

 helped to initiate the work. But the expenses incurred in London 

 only represent a fraction of the total cost of the work. Most of the 

 countries establish regional Inireaux which prepare the slips and for- 

 ward them to London. This really constitutes the most serious part 

 of the work. In Germany, for instance, the regional bureaux are under 

 Professor Uhlworm, one of the university librarians, who is hel])ed by 

 six assistants and devotes his whole time to the work. 



I pass on to an undertaking of a very different kind, but still one 

 which must be included in the class which primarily aims at cata- 

 loguing. The accurate determination of the positions of the stars for 

 a particular period is a work Avhich must precede all exact measurements 

 of their proper motions. Hence it constitutes a fundamental ])roblem 

 of Astronomy. Tlie multitude of stars seen on a l)right night is 

 bewildering to the casual observer. They are described in ])oetical 

 writings as innumerable, but when an actual count is made, it is found 

 that their numl)er is really moderate, and it is doubtful if more than 

 two thousand stars have ever l)een visible to the naked eye at the 

 same time. The use of the telescope considerably increases this 

 number, according to the size of the object glass or reflecting mirror 

 used. Thus, Argelander in his great star catalogue included nearly 

 :->24,200 stars which he observed through his telescope of four inches 

 aperture. The advent of photography, and the manufacture of suit- 

 able lenses to be used in connection with photography, increased the 

 astronomical output of a fine night to such an extent that it became 

 possible to make a further and very sul)stantial advance. The inter- 

 national Star Catalogue which is at present being constructed, owes 

 its origin chiefly to the hard work of Admiral Mouchez, who was at 

 the time Director of the Paris Observatory, and who became concerted 

 to the feasibility of the plan by the excellent results obtained ])y the 

 brothers Henry, the pioneers in star photography. He was assisted by 

 the energetic support of Sir David Gill, to wliom the first suggestion 

 was due. The programme of wt)rk was determined upon at an Liter- 

 national Conference which met at Paris in the year l<s<s7. Eighteen 

 observatories were to take ])art in the work, the telescopes to l)e used 

 were to have an aperture of thirteen inches, and such a focal length 

 that a millimetre on the plate corresponded to one minute of arc. 



