iv 
CONTENTS 
ASTRONOMY 
PAGE 
On the Radial Velocities of Nebulae By W. W. Campbell 8 
Preliminary Note on Nebular Proper Motions By H. D. Curtis 10 
Discovery of the Ninth Satellite of Jupiter By S. B. Nicholson 12 
Spherical Aberration in Astronomical Objectives Due to Changes of Temper- 
ature By Frank Schlesinger 13 
On the Relation Between the Proper Motions and the Radial Velocities of 
THE Stars of the Spectral Types F, G, K, and M 
By J. C. Kapieyn and W. S. Adams 14 
Critique of the Hypothesis of Anomalous Dispersion in Certain Solar 
Phenomena By Charles E. St. John 21 
An Attempt to Measure the Free Electricity in the Sun's Atmosphere 
By George E. Hale and Harold D. Bahcock 123 
Results of an Investigation of the Flash Spectrum Without an Eclipse: Re- 
gion \ 4800-6600 By Walter S. Adams and Cora G. Burwell 127 
Variability of Spectrum Lines in the Iron Arc 
By C. E. St. John and H. D. Babcock 131 
On the Radial Velocities of Five Nebulae in the Magellanic Clouds 
By Ralph E. Wilson 183 
Photographic Determination of Stellar Parallaxes with the 60-inch Re- 
flector By Adriaan van Maanen 187 
Some Problems in Stellar Photometry By Joel Stebbins 259 
On the Occurrence of the Line 4686A and the Related Series of Lines in the 
Spectra of the Planetary Nebulae By W. H. Wright 266 
Absolute Scales of Photographic and Photovisual Magnitude 
By Frederick H. Scares 309 
Confirmatory Experiments on the Value of the Solar Constant of Radiation 
By C. G. Abbot, F. E. Fowle, and L. B. Aldrich 331 
126 Parabolic Orbits of Meteor Streams By Charles P. Olivier 358 
Unsymmetrical Lines in Tube-Arc and Spark Spectra as an Evidence of a Dis- 
placing Action in these Sources By Arthur S. King 371 
The Direction of Rotation of Sun-Spot Vortices By George E. Hale 382 
Some Vortex Experiments Bearing on the Nature of Sun-Spots and Flocculi . . . 
By George E. Hale and George P. Luckey 385 
Nova Geminorum No. 2 as a Wolf-Rayet Star 
By Walter S. Adams and Francis G. Pease 391 
A Singular Dark Marking on the Sky By E. E. Barnard 394 
Radial Velocities Within the Great Nebula of Orion By Edwin B. Frost 416 
The Radial Velocities of the More Distant Stars By Walter S. Adams 417 
The Light Curve of XX Cygni as a Contribution to the Study of Cepheid 
Variation By Harlow Shapley and Martha Betz Shaplty 452 
Second Type Stars of Low Mean Density By Harlow Shapley 459 
A Notation for Use in the Discussion of Star Colors By Frederick H. Scares 481 
Distribution of Colors Among the Stars of N. G. C. 1647 aND M 67 
By Frederick H. Scares and Harlow Shapley 483 
Radial Velocities of the Planetary and Irregular Nebulae 
By W. W. Campbell and J. H. Moore 496 
A Statistical Study of the Visual Double Stars in the Northern Sky 
By Robert G. Aitken 530 
Outline of a Proposed System of Classification of the Nebulae by Means of 
Their Spectra ByW.H. Wright 590 
Some Probable Identities in Wave-length in Nebular and Stellar Spectra . . . 
By W. H. Wright 596 
