Sir David Brewster on the Colours of Natural Bodies. 471 
rious characters, I have given those in which I have made the 
experiments with most care. [Excepting where it is otherwise 
mentioned, the green fluid was extracted from the leaves: 
White Lilac. Celastrus scandens. 
— Convolvulus. Viburnum Tinus. 
Tulip-Tree. Prunus Lusitanica. 
Mignionette. Aucuba Japonica. 
Common Pea. Juniperus communis. 
Daphne Cneorum. Camellia Japonica. 
Virginian Raspberry. _—_ The green berries of the 
White Jasmine. Convallaria multiflora. 
Thuja occidentalis. The green berries of the 
Arbutus Unedo. Asparagus officinalis. 
Hemerocallis flava. 
When the green fluid obtained from these plants has stood 
for three or four days, it loses its high green colour, and be- 
comes of an olive-green, which grows more and more of a 
brownish-yellow, till it becomes almost colourless. During 
these various changes, the specific action of the fluid upon the 
spectrum changes also; but neither the change of colour nor 
the change of action has any relation whatever to the effects 
of an increase or decrease of thickness in the tingeing corpus- 
cles, by which Sir Isaac Newton explains the changes which 
take place in the colour of leaves. When the fluid has be- 
come almost colourless like water, it still exercises a powerful 
action upon the middle of the ved space, and a faint, but still 
perceptible action, at two points of the green band. This 
curious fact may lead us to expect that transparent media may 
yet be discovered, which shall absorb different parts of the 
spectrum, while they themselves are perfectly colourless. 
This effect of course cannot take place unless the rays ab- 
sorbed compose white light. 
In the course of these experiments, I observed a very re- 
markable phenomenon, which at first sight appeared to be 
somewhat favourable to the Newtonian theory. In making a 
strong beam of the sun’s light pass through the green fluid, 
I was surprised to observe that its colour was a brilliant red, 
complementary to the green. By making the ray pass through 
greater thicknesses in succession, it became first orange and 
then yellow and yellowish-green, and it would undoubtedly have 
become blue, if it had been transmitted through a greater 
thickness of fluid. ‘This mode of producing a spectrum by 
reflexion from the particles of a fluid, exhibits the phano- 
menon of opalescence in a very interesting form. Had the 
green fluid shown the same colour at all thicknesses, or had 
