SIR OLIVER JOSEPH LODGE, D.Sc., LL.D., F.R.S.
SIR JOSEPH JOHN THOMSON, O.M., M.A., Sc.D., LL.D., F.R.S.
JOHN JOLY, M.A., D.Sc., F.R.S., F.G.S.
GEORGE CAREY FOSTER, B.A., LL.D., F.R.S.

AND

WILLIAM FRANCIS, F.L.S.

"Nec aranearum sane textus ideo melior quia ex se fila gignunt, nec noster
vilior quia ex alienis libamus ut apes." JUST. LIPS. Polit. lib. i. cap. 1. Not.

VOL. XXXV.-SIXTH SERIES.
JANUARY-JUNE 1918.

LONDON:

TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.

SOLD BY SIMPKIN, MARSHALL, HAMILTON, KENT, AND CO., LD.
SMITH AND ON, GLASGOW ;-HODGES, FIGGIS, AND CO., DUBLIN ; —
AND VEUVE J. BOYVEAU, PARIS,

"Meditationis est perscrutari occulta; contemplationis est admirari perspicua.... Admiratio generat quæstionem, quæstio investigationem, investigatio inventionem."-Hugo de S. Victore.

CONTENTS OF VOL. XXXV.

(SIXTH SERIES).

NUMBER CCV.-JANUARY 1918.

Page

Lord Rayleigh on the Theory of Lubrication..

Prof. H. Nagaoka on the Calculation of the Maximum Force

between Two Coaxial Circular Currents...

1

13

Mr. J. A. Tomkins on the Nodal-Slide Method of Foco-

metry.

21

Mr. T. Carlton Sutton on the Value of the Mechanical Equi-

valent of Heat ...

27

Dr. L. Silberstein on Light Distribution round the Focus of a

Lens, at various Apertures ..

30

Mr. F. Twyman on Interferometers for the Experimental

Study of Optical Systems from the point of view of the

Wave Theory

49

Dr. M. Wolfke on a New Secondary Radiation of Positive

Rays

59

Prof. Barton and Miss Browning on Variably-Coupled Vibra-

tions: II. Unequal Masses or Periods. (Plates I. & II.).. 62

Mr. Nalinimohan Basu on the Diffraction of Light by

Cylinders of Large Radius. (Plate III.)

79

79

Prof. Sudhansukumar Banerji on Aerial Waves generated by

Impact. Part II. (Plate IV.)

97

Mr. Sisir Kuma Mitra on the Asymmetry of the Illumination-

Curves in Oblique Diffraction. (Plate V.)

112

Dr. J. G. Leathem on the Two-Dimensional Motion of

Infinite Liquid produced by the Translation or Rotation of

a Contained Solid.....

119