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COAL AS A RESERVOIR OF POWER. 
By ROBERT HUNT, F.R.S, 
T HE sun, according to the philosophy of the day, is the great 
storehouse of Force. All the grand natural phenomena 
are directly dependent upon the influence of energies which 
are poured forth without intermission from the central star of 
our system. Under the influences of light, heat, actinism and 
electricity, plants and animals are produced, live and grow, in 
all their infinite variety. Those physical powers, or, as they 
were formerly called, those imponderable elements, have their 
origin in one or other of those mysterious zones which envelope 
the orb of day, and become evident to us only when mighty 
cyclones break them up into dark spots. Is it possible to 
account for the enormous amount of energy which is constantly 
being developed in the sun ? This question may be answered 
by saying, that chemical changes of the most intense activity 
are discovered to be for ever progressing, and that to these 
changes we owe the development of all the physical powers 
with which we are acquainted. In our laboratory we establish, 
by mechanical disturbance, some chemical phenomenon, which 
becomes evident to our senses by the heat and light which are 
developed, and we find associated with them the principle 
which can set up chemical change and promote electrical 
manifestations. We have produced combustion, say, of a 
metal, or of a metallic compound, and we have a flame of a 
colour which belongs especially to the substance which is being 
consumed. We examine a ray of the light produced by that 
flame by passing it through a prism, and this analysis informs 
us that coloured bands, having a fixed angle of refraction, are 
constant for that especial metal. Beyond this, research 
acquaints us with the fact that, if the ray of light is made to 
pass through the vapour of the substance which gives colour to 
the flame, the lines of the spectrum which were chromatic 
become dark and colourless. We trap a ray of sunlight and 
we refract it by means of a spectroscope — an instrument giving 
