The Earl of Rosse on Lunar Heat- Radiation, 



373 



Date of 

 observation. 



Distance of 

 moon from 

 opposition. 



Altitude of 

 the moon. 



Percentage 



of moon's heat 



transmitted by 



glass. 





April 15th, 1870 

 April 1 6th 





 5 



i5 



3 1 



50 

 66 



77 



81 



93 

 109 







I 24 



I I5 



I 24 



J 19* 



\ 20 



50 

 44 

 32 

 I 44 

 I 16 

 30 

 27 



I3'3 



1 6-6 



i4'5 

 14-6 



IO'O 



IO'O 



7'i 

 8-4 



9'3 

 no 



II'O 



I2'0 



I 3'° 



I. 



II. 

 III. 



I. 

 II. 



I. 

 II. 



I. 

 II. 



April 1 7th 



March 13th 



February 10th ... 

 February 9th 



April 9th 



April 8th 



March 8th 





Mean 



The same plate of glass which was used in I. and II. on April 

 15th, and in the experiments on the two following nights, was tested 

 for the solar rays, and the following values of the percentage of 

 heat transmitted were obtained : — 



April 1 5th 



86-2 

 86-6 

 89-3 

 84-3 

 87-1 



86-8 



April 1 8th 



Mean on April 1 8th 





The piece of glass used on the other occasions, instead of being 

 placed at six or eight inches from the pile, was laid against the end 

 of the protecting cone, or about half an inch from the face of the 

 pile. When it was placed in this position and tested for solar rays, 

 an increase of deviation in the proportion of 1 • 1 to 1 was obtained, 

 owing to the "bottling up" of the sun's rays as in an ordinary 

 greenhouse, and the keeping off of currents of air. 



It seems therefore to be clearly proved that there is a remarkable 

 difference between the sun's and the moon's heat in regard to their 

 power of passing through glass. The amount transmitted varies from 

 night to night ; and in the later observations the value was generally 

 larger than in the earlier ones. Possibly this may have arisen from 

 the formation of a slight and imperceptible film of moisture on the 

 surface of the glass, which was much more unlikely to form during 

 the much shorter period* of exposure to the night air in the later 

 observations. 



* About 12 minutes in place of 30 to GO minutes. 



