II. MINERALS, ETC. 899 



3507. Sohncke's Universal Model of the Haumgitter, 



made by Heckmann of Carlsrulie, for explaining the author's 

 theory of the structure of crystals. 

 Appendages to the model : 



Key. 



12 elastic spiral threads. 



6 tin caps. Prof. Sohncke, Carlsruhe. 



3508. Model of Octahedral " Raumgitter." 



Prof. Sohncke, Carlsruhe. 



According to Bravais the molecules of all crystals are so arranged that 

 their centres of gravity lie in the intersection of three co-ordinates originating 

 in parallel equidistant planes forming a grating in space, the so-called Raum- 

 gitter of the author, who has further shown that any unlimited regular system 

 of points in space may he reduced to one or more parallel systems of this 

 kind. 



The model consists of a series of parallel tuhular brass rods arranged as a 

 cube, but which can be lengthened by sliding joints and their angles of inter- 

 section may be varied by hinged joints. The intermediate parallel gratings 

 are represented by wires carrying wooden balls which can be shifted to repre- 

 sent the required position of the molecule. With it the 14 possible kinds of 

 positions as defined by the author may be demonstrated. 



For a complete description see the author's paper in Carl's Repertorium fur 

 Experimental Physik, &c., Munich, Vol. XII. 



The universal model of the raumgitter has the object of bringing to view 

 the 14 possible different kinds of Raumgitter or point systems of the parallel- 

 epiped form. 



Its importance consists in the following points : 



(1.) According to Bravais the molecules of all crystals are arranged in a 

 Raumgitter. 



(2.) According to a theory of crystal structure, developed a short time ago by 

 the exhibitor, the molecules are arranged according to regular systems of points, 

 which latter are always composed of many Raumgitters placed in each other. 



From this one model all Raumgitters can be derived ; it is made so as to 

 be movable. The dimensions can be altered by drawing out eight edges, 

 after the manner of a telescope. Also, the globe must be divided in similar 

 proportion to the edges. 



For the purpose of altering the angles, each angle is provided with two 

 joints, by means of one of which it is possible to incline the four unlen^then- 

 able edges, which are now vertical. The four horizontal edges must previously 

 be placed parallel to each other. 



Elastic threads are sent which can be stretched between different globes to 

 show their lines of combination. The tin caps are used for indicating par- 

 ticular spheres. 



The fixed model shows the octahedral Raumgitter ; of course the movable 

 model can be brought to this form. 



3509. Case, containing 15 Models of the most impor- 

 tant Diamonds, made with Bohemian crystal glass, Koh-i-noor 

 in former and present state, Regent, Pole Star, Orlow, Empress 

 Eugenie, South Star, Nassak, Great Mogul, Tosseau, Piggot, 

 Saucy, Shah of Persia, Hope, Pasha of Egypt. 



Dr. Th. Schuchardt, Gorlitz. 



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