H. MINERALS, ETC. 755 



PYRAMIDAL AND RHOMBOHEDBAL SYSTEMS. UNIAXIAL. 



1. Calcite negative plane polarized analyzer and polarizer parallel. 



2. 45 apart. 

 3- 90 



4. elliptically polarized 45 

 Axis of ^ wave film inclined about 22| to plane of polarizer. 



5. Quartz rotary polarization. Analyzer and polarizer. 90 apart. 



6. Two similar plates of quartz superposed, the lower showing left-handed 



rotary polarization, the upper right-handed analyzer and polarizer, 90 

 apart. This phenomenon is known as Ary's spirals. 



7. Quartz circularly polarized analyzer and polarizer, 90 apart, and axis of 



wave film 45 from plane of polarizer. 



PRISMATIC OBLIQUE AND ANORTHIC SYSTEMS. BIAXIAL. 



8. Nitre plane polarized analyzer and polarizer, 'parallel line joining optic 



axes = to polarizer. 



9. Nitre plane polarized analyzer and polarizer, 45 apart, line joining optic 



45 from polarizer. 



10. Nitre plane polarized analyzer and polarizer, 90 apart, line joining optic 



45 from polarizer. 



11. Nitre plane polarized analyzer and polarizer, 90 apart, line joining optic 



parallel to polarizer. 



12. Organite optic axes, widely separated, only one is seen, analyzer and 



polarizer 90 apart, line joining optic axes parallel to polarizer. 



3487. Large Wire Model, containing one example of each 

 species of simple form in the cubic system of crystallography, with 

 its corresponding hemihedral forms inscribed within a sphere of 

 the chief zone circles of the system. Rev. Nicholas Brady, M.A. 



The coloured wires indicating the junction of the faces are painted as follows : 

 Cube, vermillion ; octahedron and tetrahedron, French blue ; dodecahedron, 

 emerald green ; three-faced octahedron and 12-faced scalenohedrons, deep 

 cadmium yellow ; 24-faced trapezohedron and three-faced tetrahedrons, burnt 

 sienna ; four-faced cube and pentagonal dodecahedrons, violet carmine ; six- 

 faced octahedron and six-faced tetrahedrons and irregular 24-faced trapezo- 

 hedrons, Schele's green. On the several zone circles are marked the position 

 of all the poles of the chief forms of the cubic system, except those of most 

 of the forms of k.k.L, or six-faced octahedron, which lie in the triangles made 

 by the zone circles. This model contains more than 700 wires soldered 

 together. Made by contributor. 



All these above forms are shown in solid in their corresponding colours in 

 the accompanying large series of models of the cubic system, and are drawn 

 in plan and perspective on a series of diagrams similarly coloured. 



The particular forms contained in this model are 100.111 + and Kill. 

 110. 122. + and - K 122. 112. + and- K 112. 210+ and r210.531+ and 

 TT 351 + and K 351. Miller's Terminology. 



3488. Collection of Models of the Cubic System of 



Crystallography, to a scale of three inches for the circum- 

 scribing cube, made in cardboard, and painted according to their 

 simple forms. Rev. Nicholas Brady > M.A. 



These comprise all the chief varieties of the several species, both holohedral 

 and hemihedral, together with the chief combinations of the principal examples 

 of each simple form, with the cube, octahedron, tetrahedron, and rhombic 

 dodecahedron, fully illustrating the passage of one combination to another. 

 In this series the positive and negative hemihedral forms and their orientation 

 are denoted by the dark and light tints of the same colour. 



3 B2 



