II. MINERALS, ETC. 897 



hedral forms, showing their orientation and combination with the 

 form 111 written. Made by contributor. 



Rev. Nicholas Brady, M.A. 



3493. Large Models of Crystals, for lecture illustration. 



Prof. Crum Brown, University of Edinburgh. 



The models are made of pasteboard, and painted. Six models are sent 



(1) Khombic Dodecahedron, and (2) Pentagonal Dodecahedron, illustrating 



the relation of these forms to the cube ; (3) and (4), Dextro and Laevo- 



tartaric acid; (5) Double laevo-tartrate of soda and ammonia; (6) Asparagine. 



3494. Collection of 1 14 Models of Crystals, in woo;l. 



Heinrich Piel, Bonn. 



3495. Collection of 100 Models of Crystals, in wood, to 

 illustrate the most important chemical compounds. 



Heinrich Picl, Bonn. 



3496. Complete collection of Models of Crystals, 300, in 

 three boxes. Heinrich Piel, Bonn. 



The whole of the collections of the models of crystals have been carefully 

 prepared by hand, without the aid of machinery. 



The models of these collections have an average diameter of section of 

 5 centimeters ; if required, the models may also be procured of a sectioit 

 of 10 centimeters, by which the price would be proportionately increased. 

 Besides complete collections of any desired size and number, single models 

 may also be obtained, the price of which will depend on the number of faces 

 and the difficulty of their manufacture. If desired, stands may be obtained. 

 Stands may.be procured for exhibiting the models in a position parallel with 

 their axes. Each collection is accompanied by a catalogue containing, besides 

 the name of the model, its form and its crystallographic symbol according to 

 Naumann's or also, if desired, according to Miller's system ; and, in 

 addition to these, the most important minerals and chemical compounds 

 which the models represent. 



3498. Eighteen large Diagrams of Crystals. 



Prof. G. com Rath, Bonn. 



These diagrams are manuscript drawings, and are used for the illustration 

 of mineral ogical and crystallographical lectures. 



3499. Models of Crystals, made from glass plates. 



IV. Apel, Gottingen. 



The large size of the models renders them especially useful for demon- 

 stration. The angles agree with those of the natural crystals, as exactly 

 as the difficulty of manufacture will permit. The threads showing the axes 

 have the same colour for similar axes, and a different colour for dissimilar 

 axes. In the hemihedral forms the corresponding holohedral forms are in- 

 cluded, and from the colours marked on them it can be seen whether they 

 are disappearing or remain in the hemihedral forms. The hexagonal systen* 

 is, according to Miller, referred to three axes cutting each other at oblique but 

 equal angles. 



3500. Models of Crystals, in wood and wire. 



Royal Mining Academy, Freiberg, Saxony* 



3501. Tables for Instruction in Crystallography. 



Dr. F. Pfafffy Th. Biasing's Library, Erlangen. 

 40075. 3 L 



