CONTENTS OF VOL. XV. SIXTH SERIES. Vll 
Page 
Mr. C. E. Van Orstrand on Inverse Interpolation by Means 
of a Beversed Series 628 
Mr. R. D. Kleeman on the Different Kinds of y Rays of 
Radium, and the Secondary y Rays which they produce . . 638 
Prof. "W. H. Bragg and Dr. J. P. V. Madsen on an Experi- 
mental Investigation of the nature of the y Rays 663 
Notices respecting New Books : — 
Dr. A. N. Whitehead's The Axioms of Projective 
Geometry and the Axioms of Descriptive Geometry . . 676 
Drs. W. H. Young and G. C. Young's Theorv of Sets 
of Points ". 676 
NUMBER XC— JUNE. 
Lord Rayleigh on Hamilton's Principle and the Five Aberra- 
tions of von Seidel , 677 
Lord Kelvin on the Problem of a Spherical Gaseous Nebula. 687 
Prof. A. Morley on Laterally Loaded Struts aud Tie-rods . 711 
Prof. A. S. Eve on the Changes in Velocity, in an Electric 
Eield, of the a, (3 and Secondary Rays from Radioactive 
Substances 720 
Mr. S. Russ on the Electrical Charge of the Active Deposit 
of Actinium 737 
Messrs. G. Owen and A. LI. Hughes on Molecular Aggre- 
gations produced in Gases by Sudden Cooling 746 
Prof. A. "W. Porter on the Effect of the Position of the 
Grating (or Prism) upon the Resolving Power of the 
Spectroscope 762 
Prof. G. H. Bryan on certain Dynamical Analogues of Tem- 
perature Equilibrium 765 
Notices respecting New r Books : — 
Bulletin of the Bureau of Standards, Washington .... 768 
Intelligence and Miscellaneous Articles : — 
On the Mixing of Gases, by S. H. Burbury 768 
Index , 788 
