REPORT OF COMMITTEE ON OBSERVATORIES 27 



there is promise of fruitful generalization, the case maybe different. 

 It so happens that the various motions of the stars, real and appar- 

 ent, are so involved that some means of separating their effects 

 must be devised. Now, it happens that this separation is very dif- 

 ficult when the observations of one hemisphere are considered alone, 

 while there is almost complete elimination of the interdependence 

 of assumptions as to one class of motions upon those as to another 

 when testimony is gathered from the entire sphere. To a very 

 considerable extent this is true of the relation of precession to solar 

 motion. 



Again, different forms of a general rotation of the stars have been 

 suggested. It is next to impossible to get any light on this ques- 

 tion from the facts of observation relating to one hemisphere alone, 

 because this effect is so entangled with the apparent motions caused 

 by precession and solar motion that they cannot be accurately dis- 

 tinguished. With testimony from the entire sphere, a wrong sup- 

 position as to precession or solar motion would not so seriously 

 affect the conclusion as to possible rotation, and in some circum- 

 stances scarcely at all. 



Again consider the spectroscopic measurement of the velocity of 

 the sun's motion through space. By combining the observations of 

 both northern and southern stars we obtain the motion of approach 

 contrasted with the motion of recession. If there should be anything 

 in the suspicion that all the observations of velocity may be affected 

 with some obscure source of error in common, this would be elimi- 

 nated in the combination of the two hemispheres. In general it is 

 obvious that we cannot neglect a large fraction of the sky when we 

 are dealing with problems concerning the whole universe. 



One consequence of this reasoning is that the proposed program 

 for a southern observatory has this peculiar merit : that the results 

 to be obtained are not only valuable in and for themselves, as consti- 

 tuting a needed increase in the sum of human knowledge, but they 

 increase in a marked degree the value of the facts of observation 

 already obtained in the northern hemisphere. 



It does not seem at all surprising that our colleagues, with em- 

 phatic unanimity, should have expressed the opinion that additional 

 astronomical effort at the present time can be expended to the best 

 advantage in the southern hemisphere. 



We have thus, here, an important research upon which further 

 special investigations are needed, and in reference to which it ap- 



