484 BoEDDiCKER — Oti Limar Radiant Heat. 



the radiation which we began to measure 1 hour 5 minutes before the first con- 

 tact witli the jjenumbra seemed to begin to decrease almost immediately ; and 

 even if the first observation be excluded, yet the decrease of heat seemed to begin 

 as early as 15 minutes before the commencement of the eclipse. These results 

 would appear to be particularly interesting as suggesting a terrestrial atmosphere 

 much more extensive than it has generally been supposed to be which intercepts 

 the Sun's rays of heat long before any part of the Moon has reached the Earth's 

 shadow. We would much desire another opportunity for attacking the subject. 

 As, however, it is exceedingly unlikely that the possibility of measuring the heat 

 during an eclipse under similarly favourable meteorological conditions will soon 

 recur here, and as it does not seem profitable to spend more time in getting a 

 slightly more accurate phase-curve, it seems desirable that the present communica- 

 tion should close the series. If we pursue the subject of radiant heat further, it 

 will be by making a new departure with apparatus modified so as if possible to 

 combine greater sensibility with greater freedom from extraneous influences, 

 varying also the methods, and extending the subjects and objects of investigation. 

 Dr. Boeddicker has devoted a great amoimt of time and labour to the fullest 

 reductions, and to the formation of the theoretical curve for the Moon's light, 

 possibly more than was justified by the probable errors of the observations, but as 

 the occasion was quite an exceptional one it ajjpeared best to leave nothing 

 undone to get the utmost out of the night's work. 



LuNAE Radiant Heat. 



I. — The Observations of 1888 and their Reduction. 



1. As mentioned by Lord Rosse in his introduction to this Paper, my observa- 

 tions in 1884 — the first really successful series of heat-observations during an 

 eclipse — showed the striking anomaly, that 38 minutes after the last contact with 

 the penumbra, the lunar heat still fell short of the Full Moon value by 13 "2 %. 

 Though I never doubted the reality of this very unexpected result, yet others did 

 so ; and the fact that the value for the lunar heat corresponding to Full Moon 

 could not be obtained on the same night before the beginning of the eclipse (the 

 Moon rose eclipsed, and clouds intervened till 23 minutes before the beginning of 

 the total phase), but had to be deduced from extra-eclipse observations, gave a 

 certain strength to these doubts. For it is well known how the state of the 

 atmosphere affects these observations, and renders conclusions from one night to 

 another difiicult and uncertain. It became, therefore, most desirable to carry 

 these observations on during an eclipse which could be watched at Bii-r Castle 



