258 
LIGHT AND RADIANT HEAT. 
admit only which differ in so many other respects, produce upon thermo- 
ravs^” 1 ^ 01 ms ers an ^ u P on our or g ans > ^e same sensations of heat and of 
light ? Why should they possess the same energy to form or to 
disunite combinations ? Would it not be more consistent with 
natural effects, that vision should not be operated in our eyes, 
except under certain limits of refrangibility, and that an extreme 
of this quality, either too much or too little, should render the 
N. rays alike unfit to produce the effect. These rays may, perhaps, 
be visible to other eyes than ours and may probably be so even 
to certain animals, and then the marvellous in their vision would 
disappear, or rather it would indicate a fact in the general mode 
of action of light. In a word, we may conceive the calorific 
quality and that of chemical power, to vary through the whole 
extent of the spectrum at the same time as the refrangibility, 
but according to different functions 5 so that the calorific quality 
shall be at its minimum at the violet extremity of the spectrum, 
and at its maximum at the red extremity ; while on the contrary, 
the chemical faculty being expressed by another function, 
would be at its minimum at the red extremity, and acquire its 
maximum at the violet extremity or a little beyond it. This single 
supposition, which is only the expression of the most simple of 
the phenomena, equally satisfies all facts antecedently observed, 
and it moreover gives a reason for those which M.Berard has 
established, and even anticipates them. In fact, if all the rays 
which produce these threeclasses of phenomena be light, it must 
follow that these phenomena will be subject to the law of 
polarity in its passing through Iceland crystal, or in being 
reflected from a polNhed glass at a determinate incidence j and 
when the rays shall have received these modifications, it must 
follow, that they will be reflected from another glass, if duly- 
placed for the exercise of its reflecting force upon light ; and on 
the contrary, when this force is nothing with regard to the visible 
luminous particles, the invisible light will not be reflected, j for 
the same cause, which occasions reflection to take place or not, 
appears to be exerted on all the rays whatever be their refrangi- 
bility, and consequently it must act upon the invisible rays j the 
condition of visibility or invisibility being relative to our eyes,and 
not 
