474 PHOTOGRAPHY IN THE SERVICE OF ASTRONOMY. 



adopting' a length of exposure of thirty minutes iu order to reach the 

 fifteenth magnitude. 



Another objection, perhaps more serious, is drawn from the impossi- 

 bility of utilizing such a superabundance of material. What will you 

 do, said David Gill, with the images of so many millions of stars wheu 

 once you have obtained them ? Where will ;you find enough astrono- 

 mers to make use of them f We are not in the floating island of Laputa, 

 where all men are exclusively occupied with mathematics so that it is 

 always necessary to strike them on the head with a bag containing dry 

 peas to awaken them. These remarks under their playful form are very 

 just. The answer to this was that the future would devise, without 

 doubt, processes of study more rapid than ours, and that it would not 

 be necessary to deprive our successors of treasures which cost us so 

 little to bequeath to them. In any case, Mouchez said, we would always 

 consider these plates as documents to consult, without being compelled 

 to study them in their smallest details, in the same manner as we pos- 

 sess a library or encyclopedia, not for the reading of all their volumes 

 from one end to the other, but for searching there in a given juncture 

 for the needed information. 



However, if we wish to compute the amount of labor which would be 

 necessary to utilize the data which the enterprise will furnish, limited 

 as it is by the resolutions of the congress, it will be found perhaps that 

 there was wisdom in not wishing to comprehend too much. There is 

 nothing evidently to prevent the enlargement of the scale of the enter- 

 prise at a later date, in ten or twenty years ; up to that time it may be 

 said that in limiting it the chances of success will be particularly in- 

 creased. 



The congress of 18S7, before adjournment, constituted a permanent 

 committee charged with securing the execution of its decisions, of cen- 

 tralizing the accounts, and of maintaining the associated observatories 

 in continued correspondence. This committee, in its turn, has formed a 

 bureau of nine members,* which hasalready commenced the publication 

 of a special bulletin, designed to keep astronomers constantly advised 

 of the state of advancement of the preparatory labors, the necessity of 

 which the congress had recognized. The committee will meet in Paris 

 the 15th of next September. 



The number of observatories which have promised to take part in the 

 making of a chart of the sky, and who have already ordered their pho- 

 tographic telescope, is at present sixteen. These are, outside of the 

 French observatories (Paris, Bordeaux, Toulouse, Algiers), those of the 

 Cape of Good Hope (Africa), Potsdam (Germany), Oxford and Green- 

 wich (England), Melbourne and Sydney (Australia), Helsingfors (Rus- 

 sia), San Fernando (Spain), Santiago (Chili), Eio de Janeiro (Brazil), 

 Tacubaya (Mexico), La Plata (Argentine Eepublic). The Royal Society 



* Presideut, Mouchez ; members, Christie, Duuer, Jausseu, Styuve ; secretaries, Gill, 

 Loewy, Vogel. 



