454: Scientific Intelligence. 



that there may be a connection between the monatomic reaction 

 and the negative temperature coefficient. It is possible to suppose 

 that translational velocity in the atoms might be a hindrance to 

 reaction. " If we permit ourselves the analogy of India rubber 

 balls coated with some adhesive substance, the more violent the 

 collision, the less likely it is that the balls will permanently 

 adhere." — Proc. Boy. Soc; Review by B. F. Lovelace, Anier. 

 Chem. Jour., xlix, 158. h. l. w. 



3. Interference of X-rays. — Due to the combined efforts of 

 W. Friedrich, P. Knipping, and M. Laue the vexed question 

 concerning the nature of X-rays seems to have been settled once 

 for all. Since it is a comparatively difficult matter to obtain a 

 copy of the original papers, and since the work is of fundamental 

 importance, the following account will probably not be considered 

 too detailed or lengthy. In Laue's first mathematical paper it w^as 

 shown qualitatively that if Rontgen rays are short electromagnetic 

 pulses in the ether, then certain phenomena might be expected 

 when a narrow pencil of X-rays was sent through suitable crystals. 

 The considerations in this prophetic paper w r ill be passed over 

 and attention will now be directed to the experimental facts in 

 the case. 



A portion of the primary X-rays proceeding from an anti- 

 cathode was allowed to pass through coaxial, cylindrical holes in 

 four comparatively thick lead screens. In this way a pencil of pri- 

 mary rays of small cross-section was obtained. This pencil was 

 then caused to pass through the crystal under investigation. The 

 diameter of the hole in the lead screen nearest to the crystal Was 

 usually either 0'75 mm or l-5 mms . The crystal was mounted on the 

 table of a goniometer since its orientation was found to be a 

 matter of importance. Also everything had to be lined up very 

 accurately with respect to the axis of the primary cone (practi- 

 cally a cylinder). Three photographic films and two plates were 

 placed in the following positions : One film was set up 2'5 cms in 

 front of the incidence face of the crystal with its plane at right 

 angles to the axis of the primary pencil. The two remaining 

 films were adjusted parallel to the first but at distances of 3*5 cms 

 and V cms from the emergence face of the crystal. The two plates 

 were disposed parallel to the primary pencil on opposite sides 

 of the crystal and at the same distance, 2'5 cms , from the lateral 

 faces of the specimen. Thus the pencil of primary rays registered 

 circular black spots near the middle of each of the photographic 

 films. Obviously the side plates were not struck by the primary 

 pencil. When the crystal consisted of a carefully prepared and 

 accurately adjusted specimen of zinc blende it was found, on 

 developing, that the first film and the two lateral plates showed 

 respectively only the central primary image and slight fog ; in 

 other words, nothing new or interesting. On the contrary, the 

 two films beyond the emergence face recorded a large number of 

 small dots which were distributed on circles concentric with the 

 primary image. Each circle contained four pairs of equidistant 



