Intelligence and Miscellaneous Articles. 247 



Among the lines of these spectra first observed by Bahr, and used 

 as tests, there is one of great intensity, which is readily changed 

 into a bright band in the manner described. — Liebig's Annalen, 

 August 1864. 



ON A NEW POLARIZING PRISM. BY PROF. H. W. DOVE. 



This contrivance consists of an isosceles right-angled prism of calc- 

 spar, one of whose equal sides is perpendicular and the other parallel 

 to the optic axis of the crystal, and therefore the' hypothenuse-side 

 at an angle of 45° with it. This rhombohedron-surface occupies 

 the axis of the polarizing-apparatus previously constructed by the 

 author, instead of the Nicol's prism which is otherwise placed there, 

 so that the light of a lamp, concentrated by a condensing lens, arrives 

 at the analyzing-apparatus after having suffered two refractions at 

 the equal surfaces of the prism and one total reflexion at the hypo- 

 thenuse- surface. The large quantity of light admitted by the appa- 

 ratus renders practicable the employment of the most deeply coloured 

 glasses, in order to obtain the perfectly definite separation of the 

 various homogeneous systems of rings. It can also be used with 

 advantage in the polarizing microscope, and for the production of 

 the systems of rings on a white screen by means of solar or the elec- 

 tric light. This prism, which acts like a Nicol, has been ground 

 according to my directions by M. Langhoff, the optician. — Poggen- 

 dorff's Annalen, vol. cxxii. p. 18. 



ON THE OPTICAL PROPERTIES OF CARTHAMINE. 

 BY PROF. H. W. DOVE. 



In the Proceedings of the Berlin Academy for 1857, page 209, I 

 have described a method of combining the visual impressions made 

 upon the two eyes simultaneously so as to produce the appearance of 

 a vivid chromatic lustre in substances which, when illuminated in 

 the usual way, show no trace of it. The method consists in holding a 

 piece of differently coloured glass before each eye, and looking through 

 both at a picture in which the colours of the two pieces of glass are 

 so combined that a figure is executed in one colour upon a ground of 

 the other colour. This reminded me that the so-called shot silks, in 

 which the warp and weft are of different colours, as well as the 

 wings of certain beetles, and, lastly, the dichroic platinum-compounds 

 examined by Haidinger, especially those which are of a bright green 

 by reflected light, and appear deep red by transmitted light, produce 

 the impression of a lustre which approaches very closely to that of a 

 metal. In like manner a metallic lustre already possessed by a sur- 

 face is distinctly heightened by combination with another colour, as 

 is clearly shown when the surface becomes covered with a film of 

 oxide, or is covered with a galvanic deposit thin enough to exhibit in- 

 terference tints. To the same class of phenomena belong also the 

 favourable changes in our impression of the colour of newly cast 

 statues when they are allowed to stand exposed to the atmosphere. 

 If these changes take place quickly, they soon lose in beauty through 



