190 Scientific Proceedings, Royal Dublin Society. 



1. The observations of 1888 and their reduction. 



The apparatus consisted (as in 1884) of two Thermopiles, 

 placed (with poles in reversed position) in the same circuit with 

 the galvanometer, and alternately exposed to the lunar radiation, 

 which, first collected by the speculum of three feet aperture, is 

 concentrated on the piles by small condensing mirrors. The time 

 of exposure was 30 seconds for each pile. Observing was carried 

 on as far as possible uninterruptedly during the whole of the 

 eclipse. Thus, the galvanometer was read off altogether 638 

 times, and 446 values for the lunar heat (each the mean of ten 

 differences of eleven consecutive readings) became available for 

 the construction of the final heat-curve. These values were cor- 

 rected for altitude, for the varying distance of the Moon from 

 Earth and Sun and finally for phase. The most probable curve 

 was then constructed. (Plates liii. and liv.. Scientific Trans. 

 E.D.S., Yol. iv., Pt. ix.) 



2. Construction of a curve representing the change of the 

 Moon's light during the eclipse. 



Assuming the Moon's and Sun's luminosities to be uniform, 

 a light-curve was constructed on the supposition that the Moon's 

 light at any given point of the Eclipse is proportional to the area 

 of the Sun as seen from the Moon at the given instant. By di- 

 viding the penumbra into 80 zones, by computing the visible area 

 of the Sun for each, and by multiplying these values with the area 

 of the Moon as cut off by the corresponding penumbral zone — a 

 curve of considerable accuracy was obtained. It is reproduced 

 with the curve of the lunar heat in per cents, of Full Moon heat 

 on Plate Iv. The same Plate gives also the corresponding curves 

 for 1884. 



3. Discussion of the observations. 



[a) . The lunar heat seems to decrease a considerable time before 

 the first contact with the penumbra. Making every allowance, it 

 seems certain that the height at which our atmosphere begins to 

 absorb solar heat cannot be less than 190 miles. 



(b). During the progress of the penumbra the heat decreases 

 more rapidly than the light. 



(c). 26-7"^ before totality the emitted heat begins to preponderate 

 over the reflected one. 



