76 



Franz Schmidt & Haensch, Berlin S. 



g) Helmholtz's Large Colour Mixing Apparatus with Lummer 

 and Brodhun's prism combination, 5 telescopes, 4 collimators with 

 bilateral slits and Rochon's prisms, polarizing arrangements before the 



slits and the observing telescope 

 with ocular slit. The apparatus 

 is shown in the German Edu- 

 cationa I Exhibition . 



h) v. Prey's and v. 

 Kries's Spectrum Apparatus 

 for mixing spectrum colours (vid 

 Report of the Physiological In- 

 stitute, in Leipzic). 



i) Colour Mixing Appa- 

 ratus, own construction, with 

 D on ders's bilateral slit. (Fig.l 3.) 



YI. Apparatus 



for demonstrating 



Spectrum Phenomena. 



(Among ,, Apparatus for ob- 

 jective demonstration"). 



YII. Auxiliary Appliances. 



There are a large number 

 of these but only the following- 

 few are of special interest: 



a) Steinheil's Hollow 

 Prisms with piano -parallel 

 sides. 



b) Wernicke's Hollow 

 Prisms, consisting of 2 crown 

 glass wedges cemented into a 

 glass box, the interspace be- 

 tween the wedges being filled 

 with cinnamomic ethylic aether. 

 The prism is protected from the 

 influence of variations of tempe- 

 rature by a wood casing. The 

 prism is remarkably transparent 

 and possesses great dispersion. 

 It is adapted both for the de- 

 flected and the rectilinear path 

 of rays. 



c) Set of Jansen's and Amici's Prisms; 3 or 4 prims. 



d) Eutherford Prisms, consisting of a flint glass and two crown 

 glass wedges; specially recommended for high dispersions. 



