508 BoEDDiCKEE — On Lunar Radiant Heat. 



eclipsed. The heat-curve consequently grows steeper, and becomes more parallel 

 with the light-curve. Finally, the decrease of heat slackens again, and the curve 

 begins to inflect, as now only the colder areas of the lunar surface reflect towards 

 the Earth. 



3. At 6^ 2-7", or 26'7". before totality, the heat-curve intersects the light- 

 curve, or, in other words, the emitted heat begins to preponderate over the 

 reflected one. The equilibrium between both kinds of heat, therefore, takes place 

 at &^ 2'7'°, when the total amount measured is about 7*3 % of the Full Moon value. 

 It is of interest to compare these facts with those observed during the former 

 eclipse. Though we can only approximately tell the point of intersection in 1884 

 (since direct observations were not obtained) there cannot be much doubt that it 

 fell at or near 21'' ir7'", or about 28 minutes before totality, when the total 

 amount of heat was 9"2 % ^^ Full Moon heat. The difference was to be expected, 

 and is evidently mainly — if not exclusively — due to the greater magnitude of the 

 more recent eclipse. It is, however, to be remarked here, that the heat observed 

 in 1884 before totality is almost certainly too small, as observations were 

 repeatedly interrupted by clouds. Thus it becomes probable, that the intersection 

 between the two curves in 1884 took place somewhat earlier than assumed above, 

 though, of course, an estimate which shall come nearer the truth cannot now be 

 given. 



4. In examining the hypothetical heat-curves during totality (see also page 505) 

 the striking point is this, that during both eclipses the last residuum of heat must 

 have been very small. The probable minimum falls in 1888 about two minutes 

 before the end of totality with about 0*4%, and in 1884 about ten minutes before 

 the end of the total phase with about 1 %. This small residuum would evidently 

 represent emitted heat only — its amount is so slight that its reality is somewhat 

 doubtful. It also falls to such an extent below the probable error of the obser- 

 vations, that it would certainly not have been perceptible to our apparatus in its 

 present construction had direct observing been practicable. Yet the character of 

 the curves on Plate LV. seems to give sufficient evidence that the lunar heat was 

 at no time actually reduced to zero. Referred to the times counted from the 

 middle of the eclipse, we have in 1884 a lagging of the heat-minimum behind the 

 light-minimum of about 35 minutes, in 1888 of about 45 minutes — a difference 

 again due to the different durations of the two eclipses. From these remarks it 

 would have been expected that the heat-values before the middle of the eclipse 

 in 1884 should have been larger (instead of smaller) than the corresponding 

 quantities of 1888. This anomaly may find its explanation in what has been 

 said in the preceding paragraph about the uncertainty of the observations made in 

 1884 before the beginning of the total phase. 



