797 



of the fiinuice. Tlioii tlio plate was fixed into the furnace, this was 

 heated to fully 300° C. and left at this temperature duriup: one hour ; 

 only after that time, the second photograph was taken. When the 

 furnace had cooled down to room-temperature, a third photog-raph was 

 taken, while the j)late remained in the furnace and in the same 

 position, as dui-ino- the heatiuf»- of it. The time of transmission 

 of the R{)NTGEN-rays was 2 or 3 hours; this was shown to be suffi- 

 cient, if a phosphorescent screen behind the photographic |)late 

 was used. The temperature of the furnace was under continuous 

 control by means of the thei-moeleinent Th. The obtained results 

 were as follows. 



Let us study first fig. 3'); it represents the image, obtained at 

 300° 0. The crystal-plate was 1 m.m. thick, and was fixed at a 

 distance of 61 m.m. from the photographic plate. Notwithstanding 

 the fact, that the normal of the crystal-pUite did not coincide abso- 

 lutely with the normal on the face of the hexahedron, one can conclude 

 from it, that the diffraction -pattern possesses a quateimy axis of 

 symmetry, — just what might be expected in each of the three possible 

 Bravais' space-lattices of the regular system. 



In fig. 4 the pattern is reproduced, obtained after the furiuice 

 has cooled down to room-temperature. The image is analogous to 

 that of fig. 3 in a misleading way ; however it doubtless differs from it. 

 Especially the following facts may be brought more into the fore- 

 ground : 1. in the quadrants to the right above and to the left 

 below, in the first row of spots from the centre, there are found 

 three small spots in close vicinity to each other; while at the same 

 place in the opposite , quadrants only two of these are present; 2. 

 especially in fig. 2 it is very evident, that in both the rows, which 

 are most elongated from the centre, there are only ƒ vt; spots between 

 the two dark limiting ones, if the rows are situated at the opposite 

 ends of a vertical diameter of the plate; but in the corresponding 

 rows at the opposite ends of a horizontal diameter of the pattern, 

 there are about nine spots between the two darker ones, while the 

 spot in the midst of the row is darker than the others, and on both 

 sides accompanied by a feebler spot. On the original negative of 

 fig. 4 these differences could already be seen easily ; but much better 

 in the fig. 2, which represents the pattern obtained from a boracife- 

 plate, 1,8 m.m. thick, but at a distance of only 42,5 m.m. from the 

 photographic plate. Notwithstanding the fact, that this plate was not 

 cut absolutely parallel to the face of the hexahedron; however, the 



') We regret that tlic flguies ai'e nnly poor reproductions of the original röntgeno- 

 grams, so that some details cannot be distinguished on Ihem. 



