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XXI. 



LUNAR RADIANT HEAT, MEASURED AT BIRR CASTLE 

 OBSERVATORY DURING THE TOTAL ECLIPSE OP 

 JANUARY 28, 1888. By OTTO BOEDDICKER, Ph. D. With 

 an Introduction by The Earl of Rosse, K.P,, &c.. President of the 

 Royal Dublin Society. 



[Abstract of Faper read Febncary 18, 1891, and published in the Scientific Transac- 

 tions, EoYAL Ddblin Society, Vol. IV., Part IX. paff e iSl, with Plates liii., 

 Hv., Iv.) 



Introduction. 



The first measurements of Lunar Radiant Heat made at Birr 

 Castle were obtained by means of Thermopiles of four couples, and 

 were published in 1869. These piles were next replaced bj single 

 Thermo-couples of home manufacture, which led to the deduction 

 of a curve, generally representing the variation of lunar heat with 

 the phase. It was also proved — by the interposition of a sheet of 

 glass — that the Moon's heat contains a much larger proportion of 

 rays of low refrangibility than solar heat. At this stage the work 

 was taken up by Dr. Oopeland, who produced a reliable curve for 

 the extinction of the heat in our atmosphere, as well as a more 

 accordant phase-curve. The former results of heat-measurements 

 through glass were confirmed, a fact which, together with the 

 anomaly apparently brought out by the phase-curve, that the 

 maximum of heat seems to fall before full Moon, rendered it very 

 desirable to measure the lunar heat during an eclipse. After 

 some unsuccessful attempts to do so, two very favourable oppor- 

 tunities occurred ; one on the 4th October, 1884, the other on the 

 27th January, 1888. The observations made in 1884 were pub- 

 lished in the Transactions E,. D. S. for 1885 ; those obtained on 

 the latter occasion form the subject of the present Paper. 



