562 



Polarisation. Double Refraction. 



No. 54 674 



54674. 1 : 6. 



54,674. Polarisation Apparatus with Divided Circle, after Lippich, on trestle stand, Figure, 

 with measurable, variable, half-shadow, with tripartite Lippich Polariser. The circle 

 can be rotated by hand or micrometrically. Readings to 0.01. The apparatus is 

 nvianged for observing tubes 220 mm long. Price without observing tubes (see 

 Nos. 54,677/81) 



54,075. -- idem, for observing tubes 400 mm long; without observing tubes (see 

 Nos. 54,677/82) 



54,676. - - idem, for observing tubes 600 mm long; without observing tubes (see 

 Nos. 54,677/83) 



Observing Tubes, Fig. 5- 

 List No. 54, 

 Length mm 94. 

 



5-1,084. Gas Sodium Lamp, latest pattern, Fig. 54,670, p. 561; Bunsen burner with platinum 

 ling for taking sodium-chloride 



54,685 Spirit Sodium Lamp, similar pattern to above 



Double Refraction. 



54,686. Model of a Gypsum Membrane, after Grimsehl, for explaining the formation of colour 

 by polarisation in double-refracting substances (Ztschr. f. d. phys. u. chem. U. 18, 1905, 



p. 326, 327, Fig. 7) 



Between two glass discs representing the bounding surfaces of the Gypsum Membrane, the wave 



lines of the ordinary (red) ray having 2 l /2 vibrations and of the extraordinary (blue) ray having 



,'t vibrations are fitted in the form of sine-shaped pieces of wire. The phase displacement inside the 



'membrane is thus known. The wire waves represented on the outside are arranged to rotate. The manner 



in which the luminous ray is split up is indicated on cardboard discs. 



54,(iS7. Model shewing the passage of converging polarised Light through a Calc-spar Plate 

 out perpendicular to the optical axis, after Grimsehl (Ztschr. f. d. phys. u. chem. U. 18, 

 1905, p. 328, Fig. 8). for explaining colour formation and the Calc-spar Cross . . . 

 It is possible to show that a calc-spar plate, cut perpendicular to the optical axis, and inserted 

 in i polarised pencil of light has no influence whatever on the nature of the polarised light in a vertical 

 :tud horizontal plane, while with an incident angle of 45 those portions of the light arc extinguished 

 (in the case of parallel polarisers) in which the phase displacement amounts to */. wave length; on tin- 

 other hand, however, those luminous rays in which the phase displacement amounts to one-quaitcr 

 or ,-v whole wave length pass through without intertVrenr,- 



54,<;ss. Model showing Polarisation in double-refracting Substances, after Grimsehl, with 

 indication of the three main diiectious which are important for the formation of the 



Calc-spar Cross (Ztschr. f. d. phys. u. chem. V., 18, 1905, p. 330, Fig. 9) 



In this model the three principal rays arc simultaneously available so that no alteration needs 

 (o be made to the apparatus during the explanation. 



s. d. 



33. 0.0 



36. 5.0 



39. 10. 



1.13.0 

 1.15.0 



1.10.0 



3. 0.0 



2. 2.0 



Cl. 1634. 



