iv 
CONTENTS 
Hypothesis to Account for the Spectral Conditions of the Stars 
By C. D. Perrine 75 
Some Spectral Characteristics of Cephetd Variables 
By W. S. Adams and A. H. Joy 129 
A Study of the Motions of Forty-eight Double Stars By Eric Doolittle 137 
Studies of Magnitudes in Star Clusters, VIII. A Summary of Results Bearing 
on the Structure of the Sidereal Universe By Harlow Shapley 224 
The Smithsonian 'Solar Constant' Expedition to Calama, Chile. .By C. G. Abbot 313 
The Absorption Spectrum of the Novae ByW.S. Adams 354 
The Distances of Six Planetary Nebulae By Adriaan van Maanen 394 
PHYSICS AND ENGINEERING 
Resonance and Ionization Potentials for Electrons in Cadmium, Zinc, and 
Potassium Vapors By John T. Tate and Paul D. Foote 9 
The Validity of the Equation P = T dv/dT in Thermo-Electricity 
By Edwin H. Hall 11 
On the Equations of the Rectangular Interferometer By Carl Bar us 13 
Thermo-Electric Diagrams on the P-V-Plane By Edwin H. Hall 29 
Is a Moving Star Retarded by the Reaction of Its Own Radiation? 
By Leigh Page 47 
On Electromagnetic Induction and Relative Motion. II By S. J. Barnett 49 
The Resolving Powers of X-Ray Spectrometers and the Tungsten X-Ray 
Spectrum , By Elmer Dershem 62 
Note on Methods of Observing Potential Differences Induced by the Earth's 
Magnetic Field in an Insulated Moving Wire 
By Carl Barus and Maxwell Barus 66 
Mobilities of Ions in Air, Hydrogen, and Nitrogen By Kia-Lok Yen 91 
Thermo-Electric Action with Dual Conduction of Electricity 
By Edwin H. Hall 98 
Terrestrial Temperature and Atmospheric Absorption By C. G. Abbot 104 
Mobilities of Ions in Vapors By Kia-Lok Yen 106 
Types of Achromatic Fringes By Carl Barus 132 
Interference of Pencils Which Constitute the Remote Divergences from a 
Slit , By Carl Barus 134 
The Structure of an Electromagnetic Field By H. Bateman 140 
The Crystal Structure of Ice By Ancel St. John 193 
On the Correction of Optical Surfaces By A. A. Michelson 210 
The Depth of the Effective Plane in X-Ray Crystal Penetration 
By F. C. Blake 236 
Thermo-Electric Action with Thermal Effusion in Metals: A Correction 
By Edwin H. Hall 297 
Types of Phosphorescence By Edward L. Nichols and H. L. Howes 305 
The Interferometry of Vibrating Systems By Carl Barus 328 
On the Essence of Physical Relativity By Sir Joseph Larmor 334 
Gravitational Attraction in Connection with the Rectangular Interferometer 
By Carl Barus 338 
The General Character of Specific Heats at High Temperatures 
By Walter P. White 343 
The Rectangular Interferometer with Achromatic Displacement Fringes in 
Connection with the Horizontal Pendulum By Carl Barus 349 
