WITHIN SOLID AND FLUID BODIES. 117 
by the first stratum is by no means very abundant, and the intromitted beam, 
even after passing through one or more undispersing strata, is dispersed nearly 
as copiously as before. In the glasses and in the vegetable solutions there are no 
peculiarities which require explanation, excepting those which arise from the 
absorption of the dispersed beam in passing through the coloured medium. 
When the phenomena of internal dispersion are exhibited in coloured fluids 
and solids, the influence of absorption upon the dispersed light is very interesting. 
Previous to its dispersion the light has the same colour as the transmitted light, 
were it to emerge at that point of its path, and when viewed at an azimuth 
above 90°, a portion of the dispersed light has that colour. The quantity of light 
possessing this colour increases between the azimuth of 90° and 180°. In order 
to see this effect disembarrassed from another influence, we must make the in- 
tromitted beam parallel to the surface of the fiuid or solid, so as just to graze it. 
In this way the dispersed light is not changed in its passage to the eye after dis- 
persion. When the beam passes through the coloured medium without this 
precaution, it again suffers absorption proportional to the thickness of the coloured 
substance through which it has passed, and sometimes disappears altogether. This 
effect is finely seen in the darker solutions, which disperse a brilliant red, or a 
brilliant green light ; the colour of the former becoming yellowish green and whitish, 
while that of the latter becomes whitish yellow. 
3. On the Polarisation of Dispersed Light. 
As the dispersed light is turned from its path by reflection, and is reflected 
at angles proper for polarising it, its partial polarisation at least might have been 
anticipated. Sir Joun Herscuen viewed it through a tourmaline, and states that 
no signs of polarisation were perceived in it ; but his method of obtaining the 
blue line from light diverging from a large area of the sky, and therefore reflected 
at various angles far above and far below the polarising angle, rendered it im- 
practicable to detect its state of polarisation. The method which I adopted, of 
using a narrow cylindrical beam of strong light, affording a bright dispersed beam 
more than an inch in length, enabled me to discover its polarisation, and to in- 
vestigate its peculiarities. 
Upon examining the blue beam in the quiniferous solution with an analysing 
rhomb of calcareous spar, I found that a considerable part of it, consisting chiefly 
of the less refrangible portion of its rays, was polarised in the plane of reflection, 
while the more refrangible of its rays, constituting an intensely blue beam, had a 
different state of polarisation. 
This insulation of the bluer rays greatly increased the beauty of the pheno- 
menon, and promised to throw some light upon its cause. I was therefore anxious 
to ascertain their state of polarisation, which was not indicated by the analysing 
rhomb. With this view! transmitted through the solution a strong beam of polarised 
