1013] 



on Great Advance in Crystallography 



691 



present as the foundation of the crystal structure. These interesting 

 photographs thus afford the first 'experimental and visible proof of 

 the truth of the structure assigned to crystals by geometricians and 

 crystallographers. By the great kindness of Professor Lane it is 

 possible to exhibit the original photographs obtained with zinc 

 blende, and one just obtained with quartz, the results for which 

 Professor Laue has not yet published. Dr. Friedrich has also most 

 kindly sent four excellent lantern shdes expressly for this lecture. 



In view of this further evidence of the richness of the original 

 discovery by Sir William Crookes of the famous tube which is uni- 

 versally known by his name — producing under suitable circumstances 

 of exhaustion the cathode rays when excited by the intermittent 



Fig. 14. 



-Diagrammatic representation op Apparatus of 

 Friedrich, Knipping and Laue. 



A. Anticathodeof X-ray bulb ; B], B.2, B3, B4, Diaphragms of Lead ; K, Leaden 

 liox screen with tubular termination R ; S, Large leaden screen ; (i, Goniometer ; 

 Pi. Pi, P3, P4, P5, Photographic plates ; Kr, Crystal ; Al, Aluminium plate. 



current from a Ruhmkorff coil, which rays, on their striking solid 

 matter such as the soda glass walls of the tube, in turn give rise to 

 the X-rays of Eontgen — it is fitting that some examples of Crookes 

 tubes should be exhibited in action, and Sir William Crookes has been 

 so very kind as to arrange a display of some of his most beautiful 

 productions, including tubes showing cathode rays impinging on a 

 diamond and a ruby respectively, with glowing phosphorescence 

 under the bombardment of the electronic corpuscles, in brilliant 

 colours in each case. By the kindness of Messrs. Newton, it is also 

 possible to exhiliit in action two recent X-ray bulbs of the particular 

 kind used by Laue and his colleagues. 



Two pictures of the actual apparatus employed (one of which is 

 reproduced in Fig. 13), most kindly also sent for the purpose of this 

 lecture, and an explanatory diagram of it (Fig. 14), will enable the 



