64 On Dispersion of Cloud under a Full Moon. 



(and similarly for first quarter, full moon, and last quarter), the 

 following results were found : — 



For the f New Moon ~\ occurring f the mean daily amount of cloud = 6*61. 



seven J First Quarter I on the J „ „ „ 672. 



days 1 Full Moon j middle 1 „ „ „ 6*76. 



having [ Last Quarter J day [ „ „ „ 6*67. 



The slight difference between the numbers is against the full- 

 moon influence, confirming a previous result. 



From the observations made at Greenwich during seven years, 

 it thus appears that the moon has not that power to disperse 

 cloud which has been ascribed to her. 



Supposing the result found for Greenwich to be also uni- 

 versally true, it may then be asked how arises any general belief 

 in the moon's influence. To answer this, let us refer to Table II. 

 It there appears that the ordinary evening change is from a cloudy 

 state of sky to a clear state of sky, also that the change is not 

 confined to any one part of the lunation, neither is it greater at 

 full moon than at other times. Towards midnight, and after 

 midnight, the ordinary tendency is again to cloud. Now the 

 period of clearance corresponds, at the time of full moon and 

 about that time only, to the period comprised between the rising 

 and advance of the moon towards the meridian. There is thus, 

 about the time of full moon, some appearance of cause and effect ; 

 for as the moon ascends above the horizon, so does the sky 

 become, on the average, finer. Further, the change from a 

 cloudy to a clear state of sky is more likely to attract attention 

 near the time of full moon ; for with no moon present the 

 general darkness is little altered, but with the moon above the 

 horizon, dissipation of the evening cloud so entirely changes the 

 aspect of nature, that the contrast between the previous dulness 

 and present splendour of the night is very striking. So that 

 the moon may, by her presence, first attract attention to the 

 evening tendency to clearance, and then, by her accident of po- 

 sition (the coincidence of her time of rising with the usual time 

 of elearance), suggest the idea that to her influence is the effect 

 remarked due. 



Such speculation, however, assumes my own result to be true ; 

 and so far as number of observations can give certainty, it ought 

 to be good. But the opposite conclusion of Sir J. Herschel is 

 stated by him (see his ' Familiar Lectures on Scientific Subjects/ 

 p. 147) to be also the result of " long-continued and registered 

 observation." And it seems difficult to suggest any probable 

 explanation of the discordance. My own result confirms my own 

 previous impression, but, being opposed to that of Sir J. Herschel 

 as well as to the belief of many people, it may be considered to 

 require confirmation by discussion of observations made at other 



