372 Royal Society : — 



and in more experienced hands their construction would be still 

 easier. 



An experiment was made with one of the piles to ascertain 

 whether, when the heat was not directed centrally on the pile, much 

 diminution of power would take place. There was less deviation, in 

 consequence of the increase of the mean distance which the heat 

 had to travel before it reached the soldering; but I believe that 

 this defect might be remedied, probably without diminution of the 

 power of the pile, by increasing the thickness of the face and 

 leaving the dimensions of the bars the same. 



"On the Radiation of Heat from the Moon."— No. II. By the 

 Earl of Rosse, F.R.S. 



In a former communication to the Royal Society I gave a short 

 account of some experiments on the radiation of heat from the moon, 

 made with the three-foot reflector at Parsonstown, during the season 

 of 1868-1869. I then showed :— • 



1st. That the moon's heat can be detected with certainty at any 

 time between the first and last quarter, and that, as far as could be 

 ascertained from so imperfect a series of observations, the increase 

 and decrease of her heat with her phases seems to be proportional to 

 the increase and decrease of her light as deduced by calculation*. 



2ndly. That a much smaller percentage of lunar than of solar rays 

 is transmitted by a plate of glass ; and we therefore infer that a large 

 portion of the rays of high refrangibility which reach the moon 

 from the sun do not at once leave the moon's surface, but are 

 first absorbed, raise the temperature of the surface, and afterwards 

 leave it as heat-rays of low refrangibility. 



3rdly. That, neglecting the effect of want of transparency in our 

 atmosphere, and assuming, in the absence of any definite informa- 

 tion on the subject, that the radiating-power of the moon's surface is 

 equal to that of a blackened tin vessel filled with water, the lunar 

 surface passes through a range of 500° F. of temperature ; conse- 

 quently "the actual range is probably considerably more. 



4thly. The proportion between the intensity of sunlight and moon- 

 light, and between the heat which comes from the sun and from 

 the moon, as deduced from those observations, agreed as nearly as 

 could be expected with the values found by independent methods, 

 and for this reason might be considered the more reliable. 



During the past season these observations have been continued : but 

 much time has been spent in trying various modifications of the ap- 

 paratus ; and a satisfactory comparison of observations made on dif- 

 ferent nights, under different circumstances, has been impossible. 

 However, by more numerous and more complete experiments, made 

 alternately with and without an interposed plate of glass, the second 

 conclusion arrived at during the previous season has been to a great 

 extent confirmed. 



The following Table gives the values found for the percentage 

 of the moon's heat which passes through glass : — 



* See Phil. Mag. vol. xxxviii. p. 317- 



