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degrees of temperature, and when the heat is intense it 
becomes visible as red, or white heat and light. The duplex 
nature of light, too, is shown by the action of the prism. 
In the spectrum, where an increase of heat appears by 
moving the thermometer from the lightest to the darkest 
or red rays, and a still higher temperature is shown when 
the bulb is placed just outside of the visible spectrum, 
viz., in the dark rays. Thus clearly proving that, by this me- 
chanical action on transmitted light among the visible rays, 
it is partially converted into heat, and wholly so converted 
outside of the spectrum or in the dark rays. We find also 
that sensible heat obeys the same laws of reflection and 
refraction that govern the motions of light, and differs only 
in the transmission through opaque or transparent bodies. 
Besides, we see the mechanical action of the lens gives direct 
proof of the conversion of light into heat by the simple con- 
vergence of its rays upon a point, whereby intense heat is 
produced. The plain inference, then, is that an element thus 
alternately exhibiting both the mingled and separate pheno- 
mena of light and heat, must possess identical properties, 
and that those several conditions of it are to be ascribed to 
the mutations of one element when subjected to the said 
acting forces. The facts adduced are clearly explained on 
this assumption, viz. — of the identity of light and heat, 
whilst they present a strange mass of anomalies, if viewed as 
produced by the movements of two distinct elements in 
space. 
I pass from mechanical action to consider the chemical 
forces, continually acting on and by this medium, whereby 
its mutations are effected, and among these, the most ex- 
tensive are caused, by the affinities between heat and water, 
as shown in common surface evaporation. Without here 
dwelling upon the diverse doctrines or views, of late enter- 
tained, respecting the nature of latent or specific heat, it 
will suffice to state the following facts, viz. — that 212° of 
