CONTENTS 
Page 
Astronomy.— Some Spectral Characteristics of Cepheid Variables 
By W. S. Adams and A. H. Joy 129 
Physics.— Types of Achromatic Fringes By Carl Barus 132 
Physics. — Interference of Pencils Which Constitute the Remote Divergences 
from a Slit By Carl Barus 134 
Astronomy.— A Study of the Motions of Forty-eight Double Stars .... 
By Eric Doolittle 137 
Physics.— The Structure of an Electromagnetic Field . . . By H. Bateman 140 
Mathematics— Invariants Which are Functions of Parameters of the Trans- 
formation By Oliver E. Glenn 145 
