CLASSIFIED CONTENTS OF VOLUMES I—VI "707 XI. OPTICS—continued. PAGE The Principle of Similitude. Art. 392. 1915 . . . Vol. VI 300 On Methods for Detecting Small Optical Retardations, and on the Theory of Foucault's Test. Art. 415. 1917 . . „ 455 Talbot's Observations on Fused Nitre. Art. 416. 1917 . . „ 471 The Theory of Anomalous Dispersion. Art. 421. 1917 . . „ 488 On the Reflection of Light from a regularly Stratified Medium. Art. 422. 1917 ....... ,,492 On the Colours Diffusely Reflected from some Collodion Films spread on Metal Surfaces. Art. 424. 1917 . . . „ 508 On the Scattering of Light by Spherical Shells, and by Complete Spheres of Periodic Structure, when the Refractivity is Small. Art.'427. 1918......„ 518 On the Scattering of Light by a Cloud of Similar Small Particles of any Shape and Oriented at Random. Art. 430. 1.918. •.......... 540 Propagation of Sound and Light in an Irregular Atmosphere. Art. 431. 1918.........,,547 On the Dispersal of Light by a Dielectric Cylinder. Art. 434. 1918...........,,554 On the Light Emitted from a Random Distribution of Luminous Sources. Art. 436. .1918.........,565 On the Optical Character of some Brilliant Animal Colours. . Art. 438. 1919............... 584 On the Possible Disturbance of a Range-Finder by Atmospheric Refraction due to the Motion of the Ship .which carries it. Art. 439. 1919......„ 597 On the Problem of Random Vibrations, and of Random Flights in One, Two, or Three Dimensions. Art. 441. 1919 . . „ 604 Ouo Dimension ......... „ 607 Two Dimensions . . . . . . „ 610 Three Dimensions ........ „ 618 On the Resultant of a Number of Unit Vibrations, whose Phases are at'Random over a Range not Limited to an Integral Number of Periods. Art. 442. 1919 . 627 Periodic Precipitates. Art. 445. 1919.....,,659 riookham's Crystals........,,661 On Resonant Reflexion 'of Sound from a Perforated Wall. Arb. 446. 1919........,,662 XII. MISCELLANEOUS On a Correction sometimes required in Curves professing to represent the connexion between two Physical Magnitudes. Art. 12. 1871........., . - Vol.1 135 45—2of a Diffusing Medium.