Aduptation of the Eye. 95 
three considerations taken jointly induce me to think that 
the moon may have an atmosphere, although such may not 
come within the range of our observation. 
Art. X.—On the Adaptation of the Eye to the Nature of the 
Rays which emanate from Bodies. By BALFOUR STEWART, 
Esq. 
In the following remarks I assume, along with Professor 
Provost, that bodies radiate at all temperatures, only the hot- 
ter bodies radiate more than they absorb, and the colder less, 
until a uniform temperature is at length attained. Now, in 
the spectrum formed by decomposing a ray of white light 
by means of a prism, the most refrangible rays are the violet 
and blue, and the least refrangible of the visible rays are the 
red; but there are yet a set of less refrangible rays, which 
though not visible to the eye, have the power of raising the 
thermometer. I conceive that all bodies at ordinary tempera- 
tures emit rays of this description, which are less refrangible 
than the extreme red of the visible spectrum, and that as the 
temperature of a body rises, the average refrangibility of the 
rays it emits rises also, and to the same extent for all bodies, 
until at almost 600° Fahr. The rays enter the visible spectrum 
by the extreme red, and the body is now said to be red-hot. 
And here I may remark, that with regard to the absolute 
identity of the heating and illuminating rays, I hold the 
opinion of Professor Powell, expressed_in his report on 
Radiant Heat, in the Transactions of the British Association 
for 1840, where he says :— 
“ The question of the identity of the heating and illumina- 
ting radiators seems clearly negatived by many experiments, 
if we mean it to apply in the sense of one physical agent; 
but, if we refer to the possibility of accounting for the 
different effects by sets of undulations of the same etherial 
medium differing their wave lengths, this probably presents 
fewer difficulties than any hypothesis of peculiar heat.” 
- However this may be, if the temperature of a red-hot body 
be still further increased, the average refrangibility of the rays 
it emits is also increased to the same extent for all bodies; 
and it is now said to be white hot. If the heat be still fur- 
ther increased, it requires a greater number of the blue or 
more refrangible rays; such, for instance, as the lime-ball 
