LIGHT AND COLOUR. 811 
diene e to laws of the same order as those which produce Lig’ht 
and Heat on the Earth. 
Although., however, we have ceased to adore the “ Central 
Orb of Fire,” we still regard the Sun with feelings of wonder. 
If our minds are freed from the thrall of superstitions by the 
development of some great truths, they are still struggling in 
the uncertainties of our imperfect knowledge, and seeking a 
deeper, a clearer insight into the vast phenomena which are 
opening upon our knowledge. 
In the absence of the Sun there is night, and when the Sun’s 
disc is obscured during an eclipse, notwithstanding the Light 
reflected from the sky, dark, unnatural shadows fall around us, 
and the colours of objects pass into neutral tints. These facts 
convince us that Light is derived from the Sun, and that the 
brilliant colours with which Nature is adorned are directly 
dependent upon luminous radiations. 
The reader, it may be, sits in a room, the decorations of 
which are in brilliant colours, the furniture to match is of the 
richest dyes, and, let us suppose, the most brilliant flowers 
of the garden have been arranged around to add to the chro- 
matic beauty. If the Light is gradually excluded, each object 
loses its colour, and eventually, if the darkening is proceeded, 
with, all becomes black. 
Another experiment is, however, necessary to carry convic- 
tion to the mind that the surfaces so richly tinctured are them- 
selves colourless, and derive all their brilliancy from the 
physical condition by which some rays of Light are absorbed, 
while others are sent back to the eye. 
We possess the power of producing flames which emit but 
one colour. Dry table-salt, if burnt in a gas-flame, or if it 
be mixed with spirits of wine and ignited, burns with a pure 
yellow light. If we make an experiment in our variedly- 
coloured room, excluding, of course, the daylight, every object 
which does not possess the power of sending back to the eye 
yellow rays, will, there being no other rays, appear of a dull 
neutral tone, or become absolutely black. 
The brilliant red fire of pyrotechnic exhibitions is produced 
by strontian. If this salt is burnt, instead of the table-salt 
( chloride of sodium), all the yellows and greens disappear, and 
those surfaces only which reflect red are seen in colour. 
The labours of the artist, the skill of the decorator, the 
technical skill of the dyer, have one end. They aim, each of 
them, at producing surfaces which shall act differently upon 
the incident rays, and thus produce different sensations on 
the organ of vision : those sensations which we call colour 
being dependent on vibrations communicated through the 
optic nerves to the brain ; these luminous vibrations present- 
