I. APPARATUS, ETC. 887 



3446. Goniometer (made by Messrs. Powell and Lealand). 

 with adjustments for mounting a crystal (as described in the in- 

 troduction) ; and with fittings adapting it for the purposes, 1, of 

 an instrument for determining refractive indices, and 2, for mea- 

 suring the angle between the optic axes of biaxal crystals. 



Prof. N. S. Maskelyne. 



3446a. Goniometer ? according to Borsch's principles ; exe- 

 cuted by Breithaupt and Son. 



High School of Industry, Cassel (Dr. E. Gerland). 



The goniometer a deflecting goniometer, according to Babinet can be 

 altered into a spectrometer by affixing a prism. It has the advantage that all 

 examinations and corrections can be ascertained without special auxiliary 

 means, as well as all angles ; refraction coefficients can be found by two 

 entirely different methods. (See Borsch, Poggend. Ann., vol. CXXIX., p. 384.) 



3447. Polarising Apparatus, with telescope tube and goni- 

 ometer. Wilhelm Steeg, Hamburg, Prussia. 



3448. Brezina's Stauroscope. 



Wilhelm Steeg, Hamburg vor der Hohc. 



3449. P. Cf roth's Universal Apparatus for Crystallo- 

 graphic Optical research. R. Fuess, Berlin. 



Vide " Physikalische Kry stall ographie," by Professor P. Groth, Leipzig, 

 Engelmann, 1876. 



3450. " Microgoniometer," for measuring -with the micro- 

 scope. P ro f> Friedrich Pfqff, Erlangen, 



The arc which stands horizontally can also be placed so that it can be 

 used for vertical measurements. A small pamphlet on the instrument 

 accompanies it. 



3451. Charles' original Goniometer. 



Conservatoire des Arts et Metiers, Paris. 



3453. Apparatus for studying and exhibiting the 

 Optical Characters of Crystals. M. Werlein, Paris. 



3454. Instruments of Observation. 



Three prisms for demonstrating the different dispersions of 



axes in crystals. 



Tourmalin pincers (Tourmalin or Lyncurium). 

 Andalusite pincers. 



Prism of dense flint ; Eossette substance. 

 Dichroismal lens. 



M. Werlein, Paris. 



