1865.] Mr. J. P. Harrison Lunar Influence on Temperature. 2.27 



rays have passed from it, still radiates the heat that has been absorbed, and 

 which it may be presumed has penetrated to a depth (according to the 

 speed with which the moon is travelling) commensurate with the time of 

 its exposure to the sun. 



Again, as regards the date of the minimum temperature of the moon, 

 doubtless the absence of all atmosphere must greatly augment the action 

 of lunar radiation ; yet it is impossible to believe that the flood of heat 

 poured iipon the moon day and night for so many days together, without 

 intermission, can be speedily dissipated. It would be more consistent with the 

 analogy of terrestrial meteorology that the state of cold in the moon should 

 be prolonged beyond the renewal of the sun's radiation, and consequently 

 no heat from her crust reach the limits of our atmosphere at first 

 quarter. 



It would be strictly according to analogy, also, if the length of time 

 which the moon's surface-crust takes to attain its maximum heat were 

 found to be greater than that which it takes in falling to its minimum. 

 Now there appears some reason to believe that this is the case ; and as the 

 mean temperature of the year attains its maximum at Greenwich about the 

 end of July (a considerable time after the summer solstice), and the day 

 of minimum mean temperature occurs in the latter half of January (the 

 intervals between the maximum and minimum, and the minimum and 

 maximum, being as 5*5 to 6 - 5), so in the tables and curves of lunar tem- 

 perature for forty-three and fifty years, a longer interval will be found 

 between the day of maximum heat at the moon's first quarter and the day 

 of minimum heat of the last quarter, than between the days of minimum 

 and maximum. Assuming, then, that the earth and the moon absorb heat 

 equally (due allowance being made for the alternate diurnal action of solar 

 and terrestrial radiation in the case of the earth, and the prolonged bi- 

 monthly alternation of solar and lunar radiation in the case of the moon), 

 if we consider the portion of the curve between the days of maximum 

 and minimum as representing the period during which the temperature of 

 the moon is increasing, and the portion of the curve between the days of 

 minimum and maximum as the period during which the temperature of 

 the moon is decreasing, the same causes operating in the case of both 

 planets, there would appear to be actual evidence of similar effects. 



Exceptions accounted for, Whether, however, the moon clears the 

 atmosphere by the agency of her radiant heat, or by thermo-electric 

 currents, or by changing the direction of the winds (a phenomenon not un- 

 frequently, perhaps, itself due to ascending currents caused by lunar radia- 

 tion), the immediate cause of the phenomenon signalized by the curves would 

 still seem to be the presence or absence of cloud and vapour in the higher 

 regions of the air, and the exceptions to the rule of a period of cloud being 

 on the average a period of heat would be owing to the varying positions 

 of the sun, the moon, and the earth, or to the fact that the formation of 



