ADVISORY COMMITTEE ON ASTRONOMY 1 25 



near approach to the earth. In 1900 occurred an opposition of this 

 planet which was more than ordinarily favorable for the determina- 

 tion of parallax. A very elaborate scheme of observations by ob- 

 servatories in cooperation was organized under the auspices of the 

 Paris Observatory. An immense mass of observations was accumu- 

 lated, especially of photographs. There seems to be a suspicion 

 that the computers are somewhat paralyzed by the very abundance 

 of material which exists in these photographic plates, contributed 

 from all parts of the world. At the Lick Observatory, as well as at 

 some others in this country, a very large number of plates was 

 secured and is now awaiting measurement and reduction. It ap- 

 pears that little or no progress in this work has been effected as yet, 

 and doubtless the Carnegie Institution may be asked to consider 

 how far and upon what principles it is willing to extend its aid in 

 carrying on this work. One is tempted to observe that zeal in tak- 

 ing photographs and reluctance in making measurements upon them 

 when taken is rather characteristic of this branch of astronomy 

 when applied to special objects. The office of the photograph is to 

 bring down the counterfeit presentment of the sky to the labora- 

 tory desk, where measurements can be made at ease. The photo- 

 graph does not eliminate the necessity for real work. It is simply 

 supposed to make the work of measurement easier. The real con- 

 tribution to science does not fairly begin until the photographs have 

 been measured, and it does not seem necessarily to follow that 

 because a stack of photographs has been taken with a certain object 

 in view, these must be measured in order to save the results to 

 science. 



Aberration of Light. 



In recent years interest in the constant of aberration was renewed 

 in a remarkable degree. Astronomers, after resting for nearly a 

 half century apparently satisfied with Struve's historic determina- 

 tion, suddenly suspected that it might be subject to serious revision. 

 For several years there has been very great activity in observations 

 and computations bearing upon this constant. The determination 

 of this constant is interesting, both from its relations to the solar 

 parallax and to the velocity of Hght. It is extremely desirable, 

 therefore, that this constant should receive the attention astron- 

 omers now seem disposed to accord to it, and that variety of method 

 should be encouraged. Recently in this country determinations 

 have been made by Professor Comstock, of Madison, employing the 



