No. 54 759. 



Gypsum, Mica and Calc-spar Preparations. 



565 



54,709. Gypsum Plates of 1 / 1 , 3 / 4 , 9 / 4 wave length; thirteen different wave retardations can be s. d. 

 produced with the same by alternating them; in round pasteboard mounts 0.15.0 



Gypsum Figures, appearing in the different colours in polarised light. 



List No. 54,710 54,711 54,712 54,713 54,714 



4 different-coloured Lamellae Cube Octahedron Star Butterfly 



0.5.0 0.6.0 0.7.0 0.10.0 0.18.0 



List No. 54,715 54,716 



Flower Bouquet 



1. 0. 1. 16. 



54.717. Double Plate after Bravais 0. 10. 



54.718. Small Gypsum Plate between two 1 / 1 mica plates, aperture 40 mm 0. 8. 



54.719. - - idem, after von Mohl, collection of 8, comprising 4 gypsum plates, read first 



to fourth order, and 4 small mica plates of 1 / 8 J /a wave-length 30 mm diameter . . 0.12.0 



54.720. Single Gypsum Plate, in 1 st order colours 0. 3. 



54.721. - - in -colours of higher order 0. 3. 



54.722. Quarter-wave Mica Plate, for investigating the character of double refraction in un- 



axial crystals, large and rectangular 0. 4. 



51.723. Gypsum and Mica Combination, after Wright, giving the most beautiful phenomena, 

 collection of 6 1. 4. 



These preparations are only suitable for Polarisation Apparatus No. 54,618. 



54.724. Mica Combinations after Norrenberg, for shewing how uniaxial mica is formed out 



of biaxial, collection of 6 pieces 1. 4. 



54.725. - - in a preparation with mica segments crossed at right angles 1. 6. 



54.726. Uniaxial circular-polarising Mica Combinations after Eeusch, left and right rotating, 

 crossed at an angle of 60 Per pair 1. 4. 



Calc-spar Preparations. 



54.693. Calc-spar Plate and Glass Plate with lettering, see Fig. 54,693, p. 563 0. 16. 



54,728. Calc-spar Prism for demonstrating decomposition and simultaneous double-refraction, 



showing two spectra (W. D. p. 452) 1. 0. 



Nicol Prisms, with oblique end surfaces: 



List No. 54,729 54,730 54,731 54,732 54,733 54,734 54,735 54,736 



Side mm 4 5 6 7 8 9 10 11 



0. 4. 0. 5. 0. 6. 0. 7. 0. 8. 0. 9. 0. 10. 0. 12. 



List No. 54,737 54,738 54,739 54,740 54,741 54,742 54,743 



Side mm 12 13 14 15 16 18 20 



0. 14. 0. 16. 1. 0. 1. 4. 1. 10. 22. 10. 3-3. 10. 



The length 01 the prisms is about 2'/ 2 times the length of side. Prices for larger Nicols quoted 

 on application. 



Glan-Thompson Prisms, with perpendicular end surfaces: 



List No. 54,744 54,745 54,746 54,747 54,748 54,749 54,750 54.751 54,752 54,753 



Length mm 15 18 20 22 24 26 28 30 35 40 



0. 10. 0. 14. 0. 18. 1. 4. 1. 12. 2. 0. 2. 10. 3. 5. 5. 10. 8. 0. 



The width is approximately hal! the length of the prism. The prices for prisms above 24 mm 

 length fluctuate. 



Mounts for Nicol Prisms with divided circle on stand, Figure. 



List No. 54,754 54,755 



For Nicols to 20 35 mm 



2. 0. 2. 10. 



54,756. Senarmont's Prism, made up of two calc-spar prisms (M. P. TI, 1, Fig. 711 [689]). I 



Prices according to size 1. 4. to 2. 0. 



Foucault Prisms (M. P. II, 1, Fig. 717 [695]), without cement, with air stratum: 



List No. 54,757 54,758 54,759 



Side mm 







20 

 1. 10. 



2. 10. 



30 

 3. 15. 



