XVI LIST OF ILLUSTRATIONS. 



CHROMATIC EFFECTS OP A PENTAGON OF UNANNEALED GLASS 



IN POLARISED LIGHT . . To face page 487 



ISOCHROMATIC LlNES IN A TRIANGLE OF UNANNEALED 



GLASS . . . '" . To face page 487 



DIAGRAM SHOWING THE COLOURS EXHIBITED BY A PLATE OF 



GELATINE WHEN EXPOSED TO A TORSIONAL SHEAR To face page 491 



