264 On the Diminution of Direct Solar Heat in the Atmosphere. 



the instruments not entirely fallacious, and heat exists in stellar 

 space. 



Professor Tyndall says, in his l Heat considered as a Mode of 

 Motion/ p. 389, " The withdrawal of the sun from any region 

 over which the atmosphere is dry must be followed by quick re- 

 frigeration. The moon would be rendered entirely uninhabit- 

 able by beings like ourselves through the operation of this single 

 cause: with an outward radiation, uninterrupted by aqueous 

 vapour, the difference between her monthly maxima and minima 

 must be enormous." If the radiation were instantaneous, 

 Mr. Glaisher's observation indicates that the surface would 

 not be heated ; it may not be safe to extend this to rough 

 surfaces, as to sand, as it is conceivable that the reciprocal radia- 

 tion among the particles may be communicated to the mass ; but 

 except on some such insecure ground as this (rejecting, as 

 before, the hypothesis of the non-existence of heat, as such, in 

 stellar space), I see no way for reconciling the above infer- 

 ence of Professor Tyndall, or the similar remarks by Herschel 

 (Outlines of Astronomy, §. 431), with Mr. Glaisher's obser- 

 vation. 



I have selected the comparison between the bright and dark 

 halves of the half moon as an example which gives a pointed 

 illustration of the difference between my view and the received 

 opinions : it seems paradoxical ; but is it contrary, not only to 

 opinions and to inferences, but to facts ? In suggesting it I con- 

 fess I see less ground for hesitation in the physical difficulty of 

 the view than in the mere fact of differing from two such autho- 

 rities as I have quoted against myself, from whom I can only 

 differ with a mental reservation that further thought and more 

 study on my part would probably bring me to adopt their con- 

 clusions. I trust that Professor Tyndall will continue to give 

 his attention to this interesting subject. 



I remain, Gentlemen, 



Your obedient Servant, 



James M. Wilson. 

 Rugby, March 10, 18G6. 



