105 



for Stand VI b 



Prices : Code- word : 



No. 182: Selenite films, Red of the I. Order, each .... Marks 4. . Peninsula. 



other Orders .... j. . 



Mica films, each ,, ^.50. 



A selenite film for Red of the I. Order generally meets all 

 requirements. 



BRAVAIS'S Double Selenite Film. In this case two semi-circular films 

 for Red of the I. Order are so arranged side by side that the equal axes of 

 optical elasticity are at right angles to each other and form angles of 45 to the 

 boundary line. 



These compound films are only supplied in conjunction with eye-pieces 

 having an adjustable eye-lens. 



Prices : Code- words : 



No. 183 : HUYGENIAN Eye-piece 2 or 3 ivith BRA VAIS Double Film Marks 30. . Penitent*. 

 184: Compensating Eye-piece 4 ivith BRAVAIS Double Film 43. . Pensadero. 



BIOT-KLEIN'S Quartz Plate, No. 185. This is a plate of quartz 3.75 mm 

 thick and cut perfectly perpendicularly to the axis. It is always supplied with 

 Stands l b and IX b and, being set in a metal mount, is handy for placing into 

 the slide fitted above the objectives of those stands. 



No. 185: BlOT-KLEIN Quartz Plate . . . Price: Marks 6. . Code-word: Pension. 



BERTRAND'S quadruple Quartz Plate. Four quadrant - shaped quartz 

 plates, cut perpendicularly to the axis, are cemented together so that their divi- 

 ding lines form the shape of a cross. Two of the plates are composed of quartz 

 with rotatory power directed to the right, the other two of crystals having the 

 opposite rotation. 



This plate is only supplied with eye-pieces having adjustable eye-lenses. 



Prices : Code- words : 

 No. 186: HUYGENIAN Eye -piece 2 or 3 ivith BERTRAND 



Quartz Plate Marks 35.. Pentagrama. 



187: Compensating Eye-piece 4 ivith BERTRAND Quartz Plate 48. . Penultfma. 



Stauroscopic Calc-spar Plate, No. 188. A plate of calc-spar, cut 

 perpendicularly to the axis, mounted so as to be readily inserted between eye- 

 piece and analyzer. 



No. 188: Stauroscopic Calc-spar Plate .... Price: Marks 7. . Code-word: Peonada. 

 For particulars of RoLLETT's Spectre-Polarizer, No. 35, see p. 32. 

 With regard to cross-line eye-pieces refer to p. 108. 



