702 Dr. Tutton on Crystallography [March 14, 



will be of the utmost benefit to him, in the sense of giving him a 

 wider grasp of the natm-e both of the particular chemical solid matter 

 under his own immediate investigation, and of the nature of solid 

 matter, the most highly organized of all the forms of matter, in 

 general. 



[A. E. H. T.] 



Appendix. 



Since this lecture was delivered, the following further experiments 

 with X-rays and ci'ystals have been described in "Nature" (1912, Vol, 91, 

 pages 111, 135, and 161). H. B. Keene has obtained with crystals of 

 galena, mica, and rock salt analogous results to those of Laue, Friedrich, 

 and Ivnipping, the spot diagrams corresponding to the holobedral system- 

 atic symmetry in each case. T. Terada has found that the transmitted 

 rays may be rendered optically visible by means of an ordinary fluorescent 

 screen, provided the pencil of rays be from 5 to 10 mm. in diameter and 

 the crystal adequately transparent to the rays ; this latter he found to be 

 the case with crystals of alum, borax, cane-sugar, fluorspar, mica, rock 

 crystal, and rock salt, in thicknesses of 4 to 10 mm. M. de Broglie has 

 obtained spot diagrams similar to those of Laue, Friedrich, and Knipping, 

 with fluorspar, magnetite (using an octahedron face), and rock salt; but 

 all the spots were striated with parallel fringes. Finally, Owen and Blake 

 have obtained what appears to be a line spectrum of X-rays by using the 

 surface of a crystal of gypsmn as a diffi-action grating. The lines were 

 always the same with different crystals, using the same X-ray bulb, but the 

 different lines varied in intensity with the hardness (degree of vacuum) 

 of the bulb. The evidence from the action of crystals on X-rays is thus 

 accumulating that the X-rays are waves of exceedingly short wave-length. 

 —A. E. H. T. 



April 22, 1913. 



