LUNAR INFLUENCE ON THE TEMPERATURE OF THE AIR. 195 



at the Royal Observatory at Greenwich, and which were published, amongst 

 other elaborate meteorological tables, in the volumes for those years. 



Out of 55 clear days, or what might be considered clear days, there enu- 

 merated — those being considered as nearly clear on which the amount of 

 cloud did not exceed *3 — no less than 42 occurred at periods of low mean 

 temperature in the lunation. And it is worth notice, in connexion with this 

 fact, that during the three years (1844, 1845, and 1846), in which the late 

 lamented Radcliffe Observer found from observations taken for the purpose, 

 between the day of first quarter and the day after full moon, "that the moon 

 was visible on an average 137 times on the meridian when the sun is seen only 

 100 times," the Greenwich Observations of cloud show an unusual number of 

 clear days to have occurred at that station on the three days following on 

 first quarter, the effects of which would appear to be traceable in the curve 

 embracing the years in question (see fig. 4). 



Still further to test the point, a curve of the mean amount of cloud in 

 November during the same seven years was formed for the purpose of com- 

 paring the approximate amount of cloud on the different days of the moon's 

 age with the line of a lunar curve of mean temperature for 40 consecutive 

 Novembers. It was hardly possible to doubt, on carefully examining the two 

 curves thus placed in juxtaposition, — the w r aves of cloud being for the most 

 part a day in advance of those of temperature, — that an intimate connexion 

 does exist, as cause and effect, between the amount of cloud at different 

 periods of the lunation and the temperature of the air. 



On the Continent, too, it was found that the results obtained by Schubler at 

 Augsburg, from 1813 to 1828, had been examined by M. Arago and admitted 

 to be in accordance with those arrived at by Flaugergues at Viviers, from 

 1808 to 1828. From a Table of the relative number of serene and clouded 

 days at Augsburg during the above-mentioned sixteen years, M. Schiibler 

 found (1) that clear days were more numerous at last quarter; (2) that the 

 greatest number of clouded days occurred towards (vers) the second octant. 

 Also in twenty-eight years at three different stations, namely at Munich from 

 1781 to 1788, at Stuttgard from 1809 to 1812, and at Augsburg as above, 

 there were 306 days of rain on the day of the first octant, 325 on the day of 

 the first quarter, 341 (the maximum) on the day of the second octant, 284 

 (the minimum) on the day of the last quarter, and 290 on the last octant. 

 Some observations which appear to have been made under M. Arago's per- 

 sonal superintendence may be quoted in confirmation of the fact, that the 

 greatest amount of cloud follows upon the moon's first quarter, and the least 

 amount of cloud on the third quarter, — 



" The discussion of the observations made at Paris led to the following 

 conclusions: — 



" The maximum number of rainy days is found to lie between the first 

 quarter and the full moon ; the minimum between the last quarter and the 

 new moon ; and the latter number is to the former as 100 is to 126*." 



4. Having pointed out, very briefly, the periods at which (taking one lu- 

 nation with another) the greatest amount of heat or cold is to be expected to 

 recur, and having also suggested a probable cause for the phenomenon, I 



* Arago's Popular Astronomy (Admiral Smyth's translation), vol. ii. p. 318. In the same 

 volume, p. 313, there is the following passage in which Sir John Herschel's explanation of the 

 moon's influence on the clouds is entirely adopted : — " In a word, provided we do not lose 

 sight of tlie fact that the rays which dissipate the clouds are cpiite different from those whose 

 calorific qualities we have been endeavouring to estimate at the instant when they reach the 

 surface of the earth, the fact which I previously called a prejudice will no longer be contrary 

 to physical laws ; and we shall obtain an additional illustration of the remark, that popular 

 opinion ought not to be rejected without eNaminatiou." 



o2 



