Adaptation 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. 



AnT. X.— O/i the Adaptation of the Eye to the Nature of the 

 Rays which emanate from Bodies. %Balfouk Stewart, 

 Esq. 



In- the followmg 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 

 bv 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:— , . . -, -n • 



The question of the identity of the heatmg 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 jctherial 

 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 increa^^ed, the average refrangibihty 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 



