[ iH ] 
CONTENTS. 
(A) 
VOL. 216. 
List of Illustrations .P a g e v 
Advertisement. vu 
I. The Monoclinic Double Sulphates Containing Ammonium. Completion of the 
Double Sulphate Series. By A. E. H. Tutton, D.Sc., M.A., F.R.S., 
President of the Mineralogical Society . page 1 
II. The Electrical Conductivity and Luminosity of Flames containing Salt Vapours. 
By H. A. Wilson, F.R.S., Professor of Physics, Rice Institute, Houston, 
Texas, U.S.A . 63 
III. The Threshold of Vision for Different Coloured Lights. By Sir W. de W. 
Abney, K.C.B., D.C.L., D.Sc., F.R.S., and Prof. W. Watson, D.Sc., 
F.R.S. . 91 
IV. On Certain Linear Differential Equations of Astronomical Interest. By Prof 
H. F. Baker, F.R.S. .‘. 129 
V. Discussion of Keiv Magnetic Data, especially the Diurnal Inequalities of 
Horizontal Force and Vertical Force, from Ordinary Days of the Eleven 
Years 1890 to 1900. By C. Chree, Sc.D., LL.I)., F.R.S., Superintendent, 
Kew Observatory . 187 
VI. On the Law of Distribution of Molecular Velocities, and on the Theory of 
Viscosity and Thermal Conduction, in a Non-uniform Simple Monatomic 
Gas. By S. Chapman, M.A., D.Sc., Fellow and Lecturer of Trinity College, 
Cambridge. Communicated by Sir Joseph Larmor, F.R.S . 279 
a 2 
