LIGHT AND RADIANT HEAT. 
25 ? 
experimental research, of which he forbears to seek the cause 
by hypothesis ; and he has constantly restricted himself to 
terms sufficiently general to allow of their being applied equally, 
whether the properties described may belong to principles of a 
nature really different and combined with light, or whether 
they may simply arise from original differences between the 
particles of one identical principle, which, according to the 
various circumstances of mass or velocity, or both united, might 
become capable of producing chemical combination, vision, or 
heat. 
Without undertaking to decide between two opinions, which They discuss 
both of them go beyond the conclusions afforded by the observed tll . e question 
facts, we may nevertheless consider their respective probabilities be three kinds 
and compare the number of hypotheses necessary in each of ^nd^having 116 
them to represent the number of facts. If we consider the solar three distinct 
light as composed of three distinct substances, of which the one * ^ 
produces visible light, the other heat, and the third effects 
chemical combinations, it must be also admitted that each of 
these substances must be separable by the prism, in an infinity 
of different modifications like light itself, because we find by 
the experiments, that each of these three principles, whether 
chemical, illuminating, or calorific, is diffused, though not in like 
proportions, over the whole of the spectrum. So that we must 
conceive in this hypothesis, that there exists as it were three spec- 
tr urns superposed one upon the other ; namely, a caloiific spec- 
trum, a chemical spectrum, and a luminous spectrum. We must 
likewise admit that each of the substances which compose the 
three spectrums, and even each of the particles of unequal 
refrangibility, which compose these substances, are endued, like 
the particles of visible light, with the property of being polariz- 
ed by reflection, of afterwards eluding the reflecting energy in 
the same positions as the luminous particles, &c. Now instead of 
this complication of ideas, let us simply conceive, agreeably to 
the phenomena, that light is composed of a collection of rays 
unequally refrangible, and consequently unequally attracted by 
bodies j which supposes original differences in their masses, 
their velocities, or their affinities. Why should these rays, 
which 
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