CHEMISTRY OF HORTICULTURE. 
101 
A variety of chemical notions have from time to time been entertained : most of these 
have passed away ; but there is one of them which, however vaguely expressed, is capable 
still of being carried to good account. Chemists of the present day are constantly in the 
habit of employing the terms element and elementary, by which they imply a substance 
that *' has hitherto resisted decomposition, or any resolution into simple forms of matter." 
The four great elements of the ancients were — fire, water, earth, and air. Now, without 
dwelling for one moment upon the absurdity of this notion abstractedly, I recur to it as 
leading to something like a consistent mode of arrangement. Elements they are not ; but 
as being the great natural agents of every phenomenon which presents itself to notice 
amidst the boundless wonders of creation, I think we cannot adopt a safer course than 
to assume them as our leaders in any attempt which may be made to convey simple 
elementary instruction. 
As concerns priority, it might be more correct to assume water as the original agent in 
the phenomena of creation ; but if potency of action be taken into the account, fire, when 
referred to its original source, must claim the precedence ; and so far, I presume, the 
Gardener will not hesitate, when I take it as the basis of that theory which has been above 
alluded to. 
The sun is, beyond doubt, the pure original foundation of light, heat, and vitality. We 
know not what the sun is, nor is it at all required that any attempt should now be made 
to inquire into its structure or composition. The telescope has plainly shown that its 
surface occasionally exhibits black spots, called maculce ; and by my own observations, 
taken on many favourable opportunities subsequent to the 12th of February, I can assert 
that, to this day (April 2nd), the solar disk has never been free from spots, which have 
been found to vary much in size and position, and to an extent that must prohibit any 
attempt thereby to ascertain the rotatory motion of the luminary. Sometimes seven to 
nine have been counted ; at others a single well-defined spot, with one or more mere 
specks, have been observed — the latter near the verge of the sphere. The only conjecture 
that has been hazarded from any appearances so erratic is, that the solar body may 
in itself be opaque, and that the macula are perforations of a luminous atmosphere 
which may enclose that dark central body. Persons have been led to form the erroneous 
opinion that the spots indicate a cold and rainy season ; yet few, we imagine, can retrace 
finer weather than that with which we have been favoured during the months of February 
and March last. 
The sun's light — pure white light — if passed through a good prism, is found to be 
divisible into seven coloured rays, which constitute the figure called the solar spectrum. 
On this point it may be gratifying to many to refer to the authority of our great philosopher, 
Sir Isaac Newton. He made a circular aperture of about one-third of an inch in the 
shutter of a dark room, and placed near it a triangular prism of highly polished glass 
(whose angle of refraction was about 64°), in a position to allow the beam of the sun to pass 
through it, and then to be received by a screen placed about eighteen feet and a half from 
the prism. This beam of light, if nothing had intervened, would have passed through the 
aperture, and proceeded onward to the screen in a straight line ; but by a power which pure 
glass possesses, the beam, on touching one of the three faces of the prism, was refracted 
or bent, and thrown upon the screen in the oblong figure called a spectrum, whose length 
was about ten inches and a half, and breadth little more than two inches. The arrange- 
ment of the coloured decomposed rays, commencing from the lowest, comprised, first, the 
red, and then, in order above it, the orange, yellow, green, blue, indigo, and violet. It 
may be made matter of conjecture whether the glass itself exerts an actual chemical 
agency upon the passing beam or not ; but such are the observable effects : and other 
chemical transparent substances, solid, fluid, and aerial, produce a powerful, though 
somewhat dissimilar effect, upon the sun's rays. It should appear, by the peculiar 
arrangement of the several tints, that they circularly blend and intermix one with the 
other ; for although the coloured image, by falling upon a perpendicular screen, conforms 
to its flat surface, yet when it is found that the blue ray at the highest end of the spectrwm 
assumes the tint of purple (called violet), it becomes highly probable that a portion of the 
