T U E 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 

 JUNE 1848. 



LIV. On the Decomposition and Dispersio7i of Light within 

 Solid and Fluid Bodies. By Sir David Brewster, K.H., 

 D.C.L., F.ItS., and V.P.R.S. Edin* 

 [With a Plate.] 



HAUYfj and other mineralogists, observed the two colours 

 which are visible in several varieties of fluor-spar. He 

 regarded the two tints as complementar}', and explained them, 

 as he did every other analogous phaenomenon, by a reference 

 to the colours of thin plates. In describing a species of di- 

 chroism noticed by Dr. ProutJ in the purpurates of ammonia 

 and potash, Sir John Herschel ascribes the green reflected 

 light§ " to some peculiar conformation of the green surfaces 

 producing what may be best termed a superjicial colour, or 

 one analogous to the colour of thin plates, and striated or 

 dotted surfaces." And he adds — " A remarkable example of 

 such superficial colour, differing from the transmitted tints, is 

 met with in the green fluor of Alston Moor, which, on its 

 surfaces, whether natural or artificial, exhibits in certain lights 

 a deep blue tint, not to be removed by any polishing." 



Having, many years ago, found the same property in the 

 Derbyshire fluor-spars, I was led to study it with particular 

 attention ; and in 1838 I communicated the results of my 

 observations to the British Association at Newcastle ||. In 

 every specimen in which the colour in question exists, I found 

 it to arise from internal^ and not from superficial reflexion. In 

 an extensive series of experiments on the absorption of light 

 by the aqueous and alcoholic solutions of the colouring matter 

 of plants, I found this property of internal dispersion in thirty 

 or forty of these solutions. The most remarkable of these 



• From the Edinburgh Transactions, vol. xvi. part 2. ReadFeb.2,184G. 

 t TraUl; de Mineralogie, torn. i. p. 512, 521. 



I Philosophical Transactions, 1818, p. 424. 

 § Treatise on Light, art. 107*3. 



II See Report of the Eighth Meeting, and Trans, of Sections, p. 10-12. 

 Phil. Mag. S. 3. Vol. 32. No. 2 1 7. Ju?ie 1 848. 2D 



