IX, MISCELLANEOUS. 213 



970. Apparatus for illustrating the Colours of double 

 refracting Bodies, in the form of a Gothic window, composed of 

 gypsum plates systematically arranged according to the colours ; 

 with a blackened glass plate belonging to it. 



Professor Dr. J. J. Oppcl, Frankfort-on-Maine. 



971. Some characteristic Drawings for illustrating the 

 Stroboscopical Principle, with manifold movements, as, for- 

 wards and backwards, centripetal and centrifugal, undulatory, 

 oscillatory, and quite irregular. 



Professor- Dr. J. J. Oppel, Frankfort-on-Maine. 



Is a collection of those principal forms of periodic movements which can 

 be represented stroboscopically. 



IX. MISCELLANEOUS. 

 97 la. Wheatstone's Apparatus. Paris Observatory. 



971b. Interferential Apparatus, by Arago. 



Paris Observatory. 



97 Ic. Curve for obtaining Wave-lengths of Spectra; and 



Map of the absorption spectra of bromine and iodine monochloride. 



Professors Roscoe and Thorpe. 



972. Mixoscope (colour-mixer), executed according to the 

 directions of the contributor by M. Ph. Edelmann, Munich. 



Prof. W. von Bezold, Royal Polytechnic School at 

 Munich. 



This apparatus permits the preparation of the true mixing colour of two 

 colours by actual trial with the brush, and thus a correct colour table can, by 

 its means, be made with greater facility than with Newton's disc. The 

 achromatised calcspar prism is so to be adjusted that on looking through the 

 apparatus only six squares should be visible. It is easy to find this position 

 through moving the telescope and turning the prism. On bringing the two 

 colours to be mixed under two of the square openings, these colours will be 

 right and left of the mixed colour, which fills the middle part of the three 

 contiguous squares. If, now, the other two apertures contain the optical true 

 mixed colour, the two central squares will appear in the same tint. 



Compare the description annexed to the apparatus. 



973. Clockwork for colour discs, for lectures with discs, 

 according to Kiihne's and Becker's principles. 



Rud. Jung, Heidelberg. 



The clockwork, provided with a strong spring, is capable of rotating 

 coloured discs of 28 centim. diameter with such velocity that a disc covered 

 with the tints of the spectrum will appear white. By a simple contrivance the 



