118 SIR DAVID BREWSTER ON THE DECOMPOSITION AND DISPERSION OF LIGHT 
light, and was surprised to find that the blue beam which it yielded by disper- 
sion, retained the same intensity in every position of the analysing prism, and 
therefore possesses a quaquaversus polarisation, such as that which light receives 
when transmitted through a congeries of minute doubly refracting crystals having 
their axes in all possible directions. 
In making the same experiment with other dispersing fluids and solids, I 
found some in which the whole beam was completely polarised in the plane of 
reflection, and others in which it exhibited solely a guaquaversus polarisation ; but 
as these experiments indicate new processes in the decomposition and polarisa- 
tion of light, which require a more extended analysis, I shall resume the subject 
in a separate communication, contenting myself at present with a general account 
of the more important facts, and the results to which they lead. 
Having transmitted a condensed beam of light through an alcoholic solution 
of the leaves of the Common Laurel, or of Tea, either green or black, I found that the 
bright red beam which it dispersed, possessed, like the b/we one in the quiniferous so- 
lution, a guaquaversus polarisation, a small portion of the light being polarised in the 
plane of reflection. The gieen beam dispersed by the preparation of orcine, has the 
same properties, the white portion of it disappearing and reappearing during the re- 
volution of the analysing rhomb. In the aqueous solution of esculine,* the dispersed 
pencil consists of two finely-contrasted pencils, the one whitish and polarised in 
the plane of reflection, and the other a very deep blue, having quaquaversus pola- 
risation. The white pencil is more intense than the blue one, which is the very 
reverse of what takes place in the solution of quinine. The alcoholic solution of 
the seeds of the Colchicum autumnale gives a bright and copious green beam of dis- 
persed light, which consists of two pencils, one whitish and polarised in the plane 
of reflection, and the other bright green, with a quaquaversus polarisation. The 
same property is possessed by a solution of guzacum in alcohol, which disperses, 
by the stratum chiefly near its surface, a beautiful violed light; and also by an 
alcoholic solution of sulphate of strychnine, which disperses a green light, after it 
has stood for some days. The same property is possessed by almost all the oils, 
in some of which the dispersed light is exceedingly beautiful, varying from a pale 
green to a blue tint. 
The polarisation of the dispersed beam in one plane, namely, in the plane of 
reflection, is exhibited in several fluids and solids. It is very marked in the bile 
of the ox, which disperses an olive-green light; in a solution of gum-myrrh in 
alcohol, diluted with water, which disperses a bright white beam; and in an 
orange-coloured glass, which disperses a pale greenish beam. 
In many fluid solutions, the beam with a quaquaversus polarisation is very 
intense, when compared with the faint pencil which is polarised in the plane of 
* In the alcoholic solution of Esculine, the faint-blue approaches to violet. The polarisation is 
like that in quinine. 
