544 



the study of trigonal and hexagonal crystals; the data relating to 

 the investigations made with tetragonal crystals will be published 

 by lis later-on in a separate coinnuinication. 



Most of' tiiese researches were executed by means of RöNTOEN-tubes 

 with platinum-anticathode, some of them, however, by the aid of 

 the CooLTDGE-tube with wolframium-anticathode and separate heating- 

 coil. In most of these experiments we used an apparatus, which 

 enabled us to make three RöNTOENOgrams (in the case of rhombic 

 crystals, by radiation along the three principal crystallographical 

 axes, or perpendicular to the tirst and second prism) at the same time. 

 This apparatus was arranged in the following way (vid. the hori- 

 zontal projection in fig. 1 p. 543). 



On a 7-shaped brass support, provided with three levellingscrews 

 S, (dimensions: 3 cm. broad, i cm. ihick, longer beam: 28 cm., 

 shorter beam: 12,5 cm.), three similar "crystal- and plate-holders" 

 D (vid. also fig. 2) were fixed in the right position by means of 

 strong screws. Every one of these bearers (fig. 2) consists of a brass 

 p bar D of 1 cm. thickness, whose 

 limiting faces are turned on the lathe 

 jjcrfeclly rectangularly and parallel 

 to each other. At the one end 

 is tixed the likewise rectangularly 

 lunied-ofï' plate-holder P, — whose 

 dimensions are 9,5 c.ra. broad, 12 cm. 

 high .lud 3 m.m. thick; at the other 

 end, however, the special crystal- 

 support K (high: 9 cm., broad: 4 cm. 

 and thick : 5 m.m.) was immovably 

 fixed by good screws. In a hole in 

 K a brass tube of 8 cm. length is 

 fixed, which is closed at both ends by (wo lead-cylinders c of 'J cm. 

 length, these being pierced along their axes by a straight canal of 



1 m.m. diameter. An accurately fitting cover A (fig. 2) can be 

 pushed on that end of the brass lube, which is next to P. its 

 front face consists of a small brass plate with a central hole of 



2 m.m. diameter. 



The crystals were smoothly pressed against (his brass plate, and 

 then held in position by means of sticking-wax. 



As a result of the careful finishing of this apparatus, one could 

 be sure, that the RöNTGEN-raj'S, after having passed the small canals 

 in the lead cylinders, progress in a thin pencil, which is perpen- 

 dicular as well to the crystal-plate, as to the photographic plate. 



Fig, 2. 



