128 
TEMPERATURE AND METEOROLOGY. 
solar beam as Light — in other words, that it consists only of that principle or power 
to which all luminous phenomena are due. Science, however, teaches us that the 
sunbeam consists of several principles, or is possessed of powers capable of producing 
several distinct phenomena, Vision and colour, calorific action, chemical change, 
molecular disturbance, phosphorescent excitation, and electrical phenomena, in their 
strange duality ; and possibly, many of the more occult forces which so mysteriously 
regulate the vital functions of plants and animals, are to be sought for in the same 
source." 
These and similar data are now announced as new; yet, if our memory and means 
of reference do not deceive us, a then nameless author, commenting upon one of 
the most striking conjectures ever hazarded by such a man as the late Professor 
Playfair, ventured, in the year 1830, to offer the following suggestions as a Theoey 
of Light : — " After mature reflection, I am inclined to define solar light as a material 
fluid, in its nature the most subtile, penetrating, and energetic — the source of all the 
phenomena of Heat, Electricity, and Magnetism. In all probability, light itself is 
in its nature subject to decomposition ; it at least exerts an inductive energy, by which 
it effects astonishing electro-chemical changes." Previously he had said, " When other 
facts," (referring to the theory of coloured rays,) " are carefully investigated, I think 
it will be found more safe to conclude that the sun's rays contain a certain principle, 
by the operation of which colours are produced and developed, than that the white 
light which comes from the sun, or from any other luminous body, is actually com- 
posed and made up of seven different kinds of light of different colours, and of such 
only. Magnetic powers are communicated to needles and small particles of steel, 
by the blue rays. The close analogy which may be traced between electricity and 
magnetism, might almost warrant the conjecture that light and magnetism, when 
under certain modifications within the earths surface, constitute electric or ele- 
mentary fire, were it not for two considerations : — First, that magnetism is pro- 
duced when concentrated electricity passes through space; and then its sphere 
of action is at right angles to the course of the electricity : thus, a bar of steel 
placed transversely over a wire, conveying an electric shock, becomes a magnet : — 
Second, that magnetism exerts its energy on iron, nickel, and some other metallic 
substances." 
In endeavouring to prove that the sun is the great natural source of all the 
vitalising agencies, the author of The Domestic Gardeners' 1 Manual adduced many — 
then — hypothetical suggestions, which modern discoveries appear to have substan- 
tiated. Thus the principles of light and heat have been separated ; and, therefore, 
if by the use of a pale-green glass, and a plate of alum, Melloni could obstruct 
nearly all the heating rays, while the same media permitted light to pass with 
freedom, we should not be surprised if, by the operation of glass surfaces, talc, 
(mica), &c, modified and coloured, as casual discoveries may dictate, the solar power 
will be, eventually, so regulated as greatly to improve the action of glazed roofs. 
The existence of two principles seems therefore to be established ; what then 
