ADVISORY COMMITTEE ON ASTRONOMY 93 



atmosphere, spectra and thermal radiation of Sun spots, distribution 

 of faculse and prominences in latitude and longitude, etc., require 

 extended research. An important investigation for which provis- 

 ion should be made relates to the amount, nature, and possible 

 variation of the total solar radiation. 



In the study of the brightness of the stars special attention should 

 be directed to the photometry of the fainter stars and the thorough 

 investigation of variable stars of long period. As all absolute mag- 

 nitudes are determined visually, further experimental researches are 

 required to solve the difficulties of measuring the brightness of stars 

 by means of photographs. The photometry of asteroids also deserves 

 attention. 



In Relation to New Instruments. 



As we have stated in the first part of this report, we consider that 

 additional assistants and computers are more urgently needed than 

 new instruments ; but it is, nevertheless, true that many important 

 advances can be made as soon as certain new instruments are pro- 

 vided. The construction of a new instrument entails the support 

 necessary for its maintenance in active investigation, and this point 

 must naturally receive consideration in connection with any pro- 

 posed grant. 



We do not feel called upon at the present time to enter upon the 

 discussion of the ownership of instruments ; this will naturally de- 

 pend upon the general policy adopted by the Trustees. Buildings 

 for housing the instruments might perhaps be provided by the in- 

 stitution to which they are supplied, but domes, which are so con- 

 structed that they can easily be transported from place to place, 

 might remain the property of the Carnegie Institution, if so desired. 

 We have thought it proper, however, to express some opinion as to 

 the general, or ideal, desirability of a few of the more important 

 projects for new instruments that have come to our attention. These 

 are matters which may be worthy of study in the future, even if it 

 should be found that they cannot be regarded as practical proposi- 

 tions at the present time. 



Respectfully submitted. 



Edward C. Pickering, Chairman. 

 IvEwis Boss, 

 George E. Hai,e, 

 Simon Newcomb, 

 S. P. Langley, 



Comtniitee. 



