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CONTENTS. 
(A) 
VOL. 221. 
List of Illustrations..P a g e v 
Advertisement . - . .. vii 
I. Some Measurements of Atmospheric Turbulence. By Lewis F. Richardson. 
Communicated by Sir Napier Shaw, F.R.S. . page 1 
II. On a Theory of the Second Order Longitudinal Spherical Aberration for a 
Symmetrical Optical System. By T. Y. Baker, B.A., Instructor Com¬ 
mander, R.N., and L. N. G. Filon, M.A., D.Sc., F.R.S., Goldsrnid Professor 
of Applied Mathematics and Mechanics in the University of London . . 29 
III. Investigations on Lightning Discharges and on the Electric Field of Thunder¬ 
storms. By C. T. R. Wilson, F.R.S.. Reader in Electrical Meteorology in 
the University of Cambridge and Observer in Meteorological Physics at the 
Solar Physics Observatory, Cambridge. (Communicated by the Director of 
the Solar Physics Observatory ). 73 
IV. Researches on the Elastic Properties and the Plastic Extension of Metals. By 
W. E. Dalby, F.R.S., Professor of Engineering at the City and Guilds {Engi¬ 
neering) College of the Imperial College of Science and Technology . . 117 
V. The Stress-strain Properties of Nitro-cell-ulose and the Law of its Optical 
Behaviour. By Prof. E. G. Coker, F.R.S., and K. C. Chakko, M.Sc., 
University College, London . 139 
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