[ iv ] 
V. The Velocity of the Ions produced in Gases by Rontgen Roys. By John Zeleny, 
B.Sc., B.A., Assistant Professor of Physics, University of Minnesota. Com¬ 
municated by Professor J. J. Thomson. F.R.S . 193 
VI. Underground Temperature at Oxford in the Year 1899, as determined by Five 
Platinum-resistance Thermometers. By Arthur A. Rambaut, ALA., B.Sc., 
Radcliffe Observer. Communicated by E. H. Griffiths, F.R.S. . . . 235 
VII. The Diffusion of Ions produced in Air by the Action of a Radio-active 
Substance, Ultra-violet Light and Point Discharges. By John S. Townsend, 
M.A., Clerk-Maxwell Student, Cavendish Laboratory, Fellow of Trinity 
College, Cambridge. Communicated by Professor J. J. Thomson, F.R.S. 259 
VIII. The Crystalline Structure of Metals. (Second Paper.) By J. A. Ewing, 
F.R.S., Professor of Mechanism and Applied Mechanics in the University of 
Cambridge, and Walter Rosenhain, B.A., St. Johns College, Cambridge, 
1851 Exhibition Research Scholar, University of Melbourne .... 279 
IX. Lines of Induction in a Magnetic Field. By Professor TL S. Hele-Spiaw, 
LL.D., F.R.S., and Alfred Hay, B.Sc .303 
X. On the Application of Fourier’s Double Integrals to Optical Problems. By 
Charles Godfrey, B.A., Scholar of Trinity , Isaac Newton Student in the 
University of Cambridge. Communicated by Professor J. J. Thomson, 
F.R.S. . 329 
XL An Experimental Investigation into the Flow of Marble. By Frank Dawson 
Adams, M.Sc., Pli.D., F.G.S., Logan Professor of Geology in McGill 
University, and John Thomas Nicolson, D.Sc., M.Inst., C.E., Head of the 
Engineering Department, Manchester Municipal Technical School (formerly 
Professor of Mechanical Engineering in McGill University) .... 3G3 
Index to Volume .. 403 
Erratum 
405 
