BoEDDiCKEE — On Lunar Radiant Heat. 483 



of glass were repeated, and they confirmed, as far as possible, the former results. 

 The phase-curve strengthened the previous impression that no appreciable interval 

 existed between the time of maximum of light and of the maximum of heat ; 

 on the contrary, from some unexplained cause the maximum of heat seemed 

 to occur somewhat before Full Moon. 



Dr. Copeland's determinations, together with his discussion of them, were 

 published in the Philosophical Transactions for 1873. 



The striking result having been arrived at that the maximum of heat did not 

 lag behind Full Moon, it appeared desirable to proceed a step further, and as a 

 more rigid test to try how far the minimum of heat, which presumably existed 

 during the progress of a lunar eclipse coincided with, or came later than the 

 middle of that eclipse. Every visible lunar eclipse was eagerly waited for. 

 The first occasion on which we were able to obtain a glimpse of the Moon during an 

 eclipse was on November 14, 1872. The eclipse was only partial. The Moon was 

 at a low and a diminishing altitude, and clouds interfered much. The heat 

 radiation was, however, observed rapidly to decline during its progress, apparently 

 as much as the light. 



On October 4th, 1884, the next favourable opportunity occurred.* Dr. 

 Boeddicker was on the spot with the apparatus in position from the commence- 

 ment of the penumbra until forty minutes after the last contact with the 

 penumbra. Clouds intervened until twenty-three minutes before totality, when 

 the sky became perfectly clear, and remained so until the end of the observations. 

 The heat as before diminished, and increased again nearly proportionally to the 

 light, becoming inappreciable on reaching the limits of totality. The minimum 

 of heat apparently fell later than that of illumination. But the most remarkable 

 thing was that while during the short interval between the first contact with the 

 penumbra and the commencement of total phase all appreciable radiation vanished, 

 between the end of total phase and the last contact with the penumbra, and even 

 forty minutes later the heat had not returned to the standard for Full Moon, being 

 deficient by about twelve per cent. This we failed to explain, where we might 

 expect to do so, by any derangement of the apparatus, nor could we trace it to 

 any physical cause. The above observations were published in these Transactions 

 for 1885 (vol. iii., series 2). 



The next opportunity, an exceptionally favourable one, occurred on January 

 28, 1888. The sky was not obscured at all during the whole progress of the 

 eclipse, and the same anomaly of the heat not returning to its standard value, even 

 1 hour 40 minutes after the last contact with the penumbra was observed. Also 



* A total eclipse had meanwhile taken place on August 23, 1877, but owing to many interruptions 

 from clouds, and the low altitude of the Moon, no advance was made. See Copernicus, vol. i., p. 22. 



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