CONTENTS 
Page 
Psychology.— Measuring the Mental Strength of an Army 
By Major Robert M. Yerkes 295 
Physics. — Thermo-Electric Action with Thermal Effusion in Metals: A 
Correction By Edwin H. Hall 297 
Mathematics.— Invariants and Canonical Forms . . . By E. J. Wilczynski 300 
Physics. — Types of Phosphorescence . . By Edward L. Nichols and H. L. Howes 305 
Astronomy.— The Smithsonian 'Solar Constant' Expedition to Calama, Chile 
By C. G. Abbott 313 
Genetics. — Maroon — A Recurrent Mutation in Drosophila 
By Calvin B. Bridges 316 
