OF ARTS AND SCIENCES. 141 



solar rays, their temperature would be considerably raised by the ab- 

 sorbed heat. The radiation of a body like the moon must consist, in 

 considerable part, of emanations from such a heated surface ; and it 

 becomes important to inquire whether our atmosphere is permeable 

 by such rays. 



Lord Rosse found, at the time of total lunar eclipse, that with tl;e 

 disappearance of the last ray of light from the vanishing moon radia- 

 tion, to which his thermopile was sensitive, vanished also. On the 

 night of January 28, 1888, the first systematic observations were 

 made by the writer and his assistants with the previously described 

 apparatus. The moon rose eclipsed. A reduction of the observations 

 shows that 



19 minutes before totality the deflection was 11.2 divisions. 



o (t tt (( it a u n o (t 



During first minute of totality " " 3.2 " 



Mean of 30 readings taken during total phase 2.09 " 



After the total phase had passed, but while the moon was still in 

 the penumbra, .254.4 was obtained as the mean of 20 readings. 



No attempt was made to observe continuously. The evening was 

 so intensely cold, that one could not stand quietly in the open air for 

 any length of time without freezing. The inference to be drawn from 

 these observations is, that all but a minute portion of the rays from 

 the lunar soil and rock are cut off by our atmosphere, for it is impos- 

 sible to conceive that a surface like that of the moon, upon which the 

 sun has been shining continuously for many days, should suddenly 

 cease to radiate upon withdrawal from the sunshine. It is very 

 questionable, then, if at any time we receive any considerable portion 

 of the radiation from the lunar rocks. 



The results given above are in substantial agreement with those 

 obtained by Dr. Boedicker during the same eclipse. He employed a 

 thermopile, and condensed the lunar rays with the three-foot speculum 

 of Lord Rosse. He says,* that, twenty minutes before totality com- 

 menced, the heat was reduced to less than five per cent of what it waa 

 before first contact with the penumbra. He also observes, that the heal 

 radiated by the moon commences to diminish long before first contact ; 

 and that the heat, after last contact with the penumbra, did not mount 

 immediately to what it had been before first contact with penumbra. 



It was intended, upon the occasion of the total lunar eclipse of July, 



* Nature, March 8, 1888. 



