liG ANNUAL OF SCIENTIFIC DISCOVERY. 



off the imai^c, and carried away its plainness. Thus the slowness 

 ot" the vibrations of the red, orange, and yellow is the cause of 

 their <jbscurity, in phot()ij^ra])Iiy as in the; crepuscule li<^ht, and 

 the ;^reater rapidity of the \ iln-ations of the blue, indigo, and vio- 

 let is the cause of their milky or cloudy appearance, as well in 

 photography as in the gliniiuer of the crepuscule. — Comptes Een- 

 dus, July 2tl, 18G9. 



A NEW POLARIZING PRISM. 



It is a trough, parallelopipedon in form, of glass fdled with sul- 

 phuret of carbon, and in which is placed, with a suital)le inclina- 

 tion, a very thin plate of spar. All natural luminous rays tend to 

 decompose in the spar into two rays, — the one ordinary, and the 

 other extraordinary ; but as the index of this last ray is inferior 

 to that of the sulpiiuret of carbon, it is totally reflected, and the 

 ordinary ray alone traverses the trough, and is polarized in the 

 plane of incidence. This apparatus replaces successfully the 

 l)rism of Nicol in all its uses ; and as it rc^quires only a very thin 

 plate of spar, it is cheap, and affords a wide lield of vision. — M. 

 Jamin. — Comptes Bendus, Feb. 1, 1869. 



COMPLEMENTARY COLORS. 



Complementary colors, by reflected and transmitted light, are 

 admirably shown by a sim])le arrangement, to which attention 

 has been called by Prof. E. C. Pickering, of Boston. A plati; of 

 glass is coated with a layer of the violet-colored ink, made from 

 aniline color, now much used, and this fluid is allowed to dry 

 ui)on it. If we then place this in such a position that light is re- 

 flected from its surface to our eyes it will ap[)ear of a nK^tallic 

 golden color, as though coated with a gold bronze ; but if we 

 look through it at the light, the color will be Ti very rich purple. 

 Tiiere are many other bodies having a similar action, but in none 

 that we know of is it so striking as in this. 



Thus, glass flashed with silver has a green color by reflected, 

 and an orange- red by transmitted light. Salts of the sesquioxide 

 of chromium, which are green by retlected, are red by transmitted 

 light; a solution of ordinary litmus is blue by reflected, but red by 

 transmitted light. — Journal of the Franklin Institute, April, 

 1869. 



ABSORPTION LINES PRODUCED BY THE PASSAGE OF THE 

 SOLAR LIGHT THROUGH CHLORINE. 



• 



Morren has found that by employing a spectroscope of 5 prisms 

 of liighlv dispersive flint-glass, alisorption lines are distinctly visi- 

 ble in the si)eetrum of light which has traversed a tube tilled with 

 chlorine two metres in length. The lines begin to be visible in 



