22 NATIONAL ACADEMY OF SCIENCES 



to show the great variety of problems in which useful results 

 have already been achieved by international co-operation, and 

 to bring the lessons of the past years to bear on the future. 

 I divide international co-operation into three categories: 

 i. Agreement on standards and units of measurement. 



2. The distribution of work bearing on the same problem, 

 between different nations, for the purpose of economizing time 

 and expenditure. 



3. The investigation of problems which can not be solved 

 unless observations made with identical or similar instruments 

 are obtained from different parts of the world and the records 

 published in a homogeneous form. 



I think all are agreed as to the question of units and I need not 

 detain you by giving you an account of the various international 

 conferences which have been held and agreements which have 

 been arrived at on these matters. 



As regards problems of the second category, they are those 

 which deal mainly with the cosmos as a whole because their 

 solution depends so much on the collection of statistics which 

 exceeds the powers of individuals or even of single nations. A 

 few examples may illustrate what has already been accom- 

 plished. First, and foremost, we have the great Star Catalogue, 

 initiated at an international congress twenty-five years ago, 

 when eighteen observatories combined to divide the work, each 

 taking a number of zones in the heavens. 



The importance of this work will be plain to everyone, and we 

 must regret that it is still so far from being completed. 



As it is not my intention simply to point out the merits of 

 international work, but also to point out its difficulties, a few 

 words may be said which are not intended as criticism, but which 

 may serve to point out the weakness which arises when there 

 is no central authority which lives longer than the single indi- 

 vidual can expect to live. 



Pioneers will always be found to initiate a work, but in time 

 they die or retire from office; others take their places, and if 

 these become more interested in fresh problems, the w r ork suffers 



