Cloud under a Full Moon. 



63 



On the average of twenty-four hours, the mean for full moon 

 scarcely differs from that for the whole period, or from that at new 

 moon. The slight difference that exists is against the supposed 

 influence. And comparing the night hours only, the means are 

 (including from 7 h 20 m to 17 h 20 m ) for full moon 6*48, for the 

 whole period 6*40, for new moon 6'07. These differences are 

 also against the supposed influence ; or the night is least clear 

 at the time of full moon. 



A further discussion of the full moon observations was made. 

 The numbers in Table II. in the column for full moon, depend on 

 observations made on 435 days. The observations on these days 

 were now arranged according to the time of moonrise on each day, 

 and the means taken. Before, however, taking the means, the 

 observations were corrected for the general diurnal inequality. 

 For the average of the whole year, corrections such as would be 

 given by Table I. would be proper to use. But as the days 

 were not quite symmetrically distributed over the twelve months 

 of the year, and as the inequality is greater in summer than in 

 winter, corrections were determined independently for each 

 month. The means finally found remain affected by very nearly 

 the whole of the full moon influence, if any exists. 



Table III.- 



-Mean Amount of Cloud from observations on 435 days at 

 Full Moon. 



Time as referred to moonrise. 



Mean amount 

 of cloud. 



Four hours ] , c . [ 

 Two hours j before moonrise ...| 



At monnrisft 



6-69 

 6-66 

 6-73 

 6-63 

 6-87 

 6-69 

 6-65 

 6-82 

 6-67 



Two hours 

 Four hours 

 Six hours 

 Eight hours 

 Ten hours 

 Twelve hours / 



( 



i 



1 

 •after moonrise -{ 



i 



The means of successive values taken twice give 6*69, 6*69, 

 672, 6-77, 6-73, 6*71, 6*75. The second value is that corre- 

 sponding to moonrise ; or, the general or solar inequality being 

 removed, there appears to be no trace of lunar influence. 



Again, if the full moon tends to disperse cloud, its amount 

 ought to be least at the full-moon quarter. In the Greenwich 

 volumes, the mean amount of cloud is given for every day as 

 deduced from the two-hourly observations. Grouping together 

 all the days of new moon with the days one day, two days, and 

 three days before, and one day, two days, and three days after 



