2o 4 SCIENCE PROGRESS 



no orbit represents the observations satisfactorily ; there are 

 either systematic errors in them or there is a third disturbing 

 body. It is shown that discrepancies are well represented on 

 the latter hypothesis. 



Stellar Clusters. — Shapley, Harlow, Studies based on the 

 Colours and Magnitudes in Stellar Clusters : 



I. The General Problem of Clusters. 

 II. 1,300 Stars in the Hercules Cluster (Messier 13). 



III. A Catalogue of 311 Stars in Messier 67. 



These papers form respectively Mt. Wilson Observatory 

 Contributions, Nos. 115, 116, 117; they are abridged together 

 in Astroph. Journ. 45, 118, 191 7. 



IV. The Galactic Cluster, Messier 1 1 ; Mt. Wilson 



Conts. 126, 191 7; Astroph. Journ. 45, 164, 191 7. 



V. Further Evidence of the Absence of Scattering of 



Light in Space, Proc. Nat. Acad. Sci. 3, 267, 191 7. 



VI. The Relation of Blue Stars and Variables to 



Galactic Planes, Proc. Nat. Acad. Sci. 3, 276, 191 7. 



It should be noted that the Proc. Nat. Acad. Sci., Washing- 

 ton, contains only brief accounts of researches, the full details 

 of which are published subsequently elsewhere. The full 

 details of the last two papers have not yet been published. 

 The above important series of papers will be reviewed together 

 when completed. Connected with them is the following : 



Pease, F. G., and Shapley, Harlow, On the Distribution 

 of Stars in Twelve Globular Clusters ; Mt. Wilson Conts. 129, 

 191 7 ; Astroph. Journ. 45, 225, 191 7. 



Stellar Distributions. — Gyllenberg, W., Distribution in 

 Space of Stars of Spectral Type O, Arkiv. for Math. Astron. 

 och. fysik k. Svenska-vetensk 11, No. 28, 191 7 ; Lund Medd. 



75, 1917. 



Malmquist. K. G., The Distances and the Velocity Dis- 

 tribution of the Stars of the Spectral Type A, Arkiv. k. Svensk. 

 etc., 11, No. 29, 191 7 ; Lund Medd. 76, 191 7. 



Lundall, C. F., Preliminary Note on Distances and 

 Velocities of Stars of Spectral Type F., Arkiv. k. Svensk., etc., 

 11, No. 30, 1917 ; Lund Medd, 77, 1917. 



These are three similar papers by students of Prof. Charlier, 



