1906.] on Inter national Science. 347 



Each observatory had a certain region of the sky assigned to it, and 

 undertook to cover this region four times, twice with plates of short 

 exposure, twice with plates of long exposure, and to measure all the 

 stars appearing on the short exposure photographs. The long expo- 

 sures were intended for reproduction in the form of charts, and are 

 only taken by some of the observatories. As there are about 400 stars 

 on each plate and it takes about 600 plates to cover the share of one 

 observatory once, this means that each observatory has to measure 

 nearly half a million star places, and that the complete catalogue will 

 give the positions of nearly four and a half million stars. This in- 

 cludes all stars down to the eleventh magnitude. 



The following is a list of observatories taking part in the work : — 



For the Northern Hemisphere : Greenwich, Oxford, Paris, Bor- 

 deaux, Toulouse, Potsdam, Helsingfors, Rome, Catania, Algiers. 



For the Southern Hemisphere: San Fernando, Tacubaya, Santiago 

 de Chile, Cordoba, Cape of Good Hope, Perth (AY. Australia), Sydney, 

 Melbourne. 



The work connected with the ultimate completion of the catalogue 

 and especially the reproduction of the star maps requires considerable 

 expenditure. Each country has to make its own aiTangements, which 

 in the British Empire usually means that each body concerned has to 

 pay its own expenses. There was, however, in this case, some official 

 help. The Astronomer Royal obtained a contribution of 5000/. from 

 the Government for the reproduction of charts, and in the case of the 

 Cape of Good Hope the necessary expenses have been met from 

 Imperial Funds. Professor Turner, of Oxford, has obtained a grant 

 of lOoO/. from the Government grant of the Royal Society, and a 

 further sum of 2000/. for publication from the Treasury and the 

 University of Oxford jointly ; l)ut the Australian Colonies are much 

 hampered by the want of funds, and their work will be delayed in 

 consequence. The four French observatories on the other hand are 

 well supported. Each of them has received a Government contribu- 

 tion of 25,700/., making a total of well over 100,000/. More than 

 half this goes towards the reproduction of the long exposure photo- 

 graphs as a series of charts, which, however, have proved to be so 

 costly that they will j^robably never be completed. Indeed, if com- 

 pleted, their utility may to some extent be impaired by the difficulty 

 of storing them in an accessible manner. Professor Turner calculates 

 that the series of maps will form a pile of papers 80 feet high, weigh- 

 ing about two tons. 



I now pass on to a few examples of undertakings which are 

 intended to fix standards of measurement, or to establish a general 

 agreement on matters in which uniformity is desirable. The foremost 

 place in this division must be given to the Bureau International des 

 Poids et Mesures, established in the year 1873, at Sevres, near Paris. 

 This bureau was the outcome of an international commission con- 

 stituted in 1869, which had for its object the scientific construction of 



