CONTENTS 
Page 
Psychology. — Personal Equation and Steadiness of Judgment in the Esti- 
mation OF the Number of Objects in Moderately Large Samples . . . 
By J. Arthur Harris 65 
Chemistry. — Polypeptide-Hydantoins By Treat B. Johnson 69 
Botany. — Recent Explorations in the Cactus Deserts of South America . 
By /. N. Rose 73 
Astronomy. — On the Albedo of the Planets and Their Satellites .... 
By Henry Norris Russell 74 
Physics. — Quantum Relations in Photo-Electric Phenomena 
By R. A. Millikan 78 
Chemistry. — The Chemical Activity of the Ions of Hydrochloric Acid De- 
termined by Electromotive Force Measurements . . By James H. Ellis 83 
Zoology. — Effects of Centrifugal Force on the Polarity of the Eggs of 
Crepidula By Edwin G. Conklin 87 
Physics. — The Emission Quanta of Characteristic X Rays . By David L. Webster 90 
Geology. — ^The Results of Investigations of the Ecology of the Floridian 
AND Bahaman Shoal-Water Corals . . . By Thomas Wayland Vaughan 95 
Paleontology. — Cambrian Trilobites By Charles D. Walcott 101 
Astronomy. — ^The Minute Structure of the Solar Atmosphere 
By George E, Hale and Ferdinand Ellerman 102 
Astronomy. — Monochromatic Photography of Jupiter and Saturn .... 
By R. W. Wood 109 
