4 
POPULAR SCIENCE REVIEW. 
In the account of the famous experiments upon the mountain 
top made in 1856, this observer states that “on Gruajura there 
appeared to be a strong tendency to upper clouds during several 
days preceding full moon, but on that night every particle of 
them disappeared : the lower clouds, however, were constant 
through the whole lunation. This does seem to confirm Sir 
John’s idea; and to show, too, that the moon’s heat, though 
effective at great heights, is entirely expended before arriving at 
the lower strata of cloud, 2,300 feet above the sea. The elevation 
of the upper clouds, which were apparently so effectually acted 
on, we had no means of accurately judging of ; but I should 
suspect that it could not have been less than 15,000 feet.” * 
Now, Buys Ballot pointed out, in 1847, that this absorption 
of heat by the higher airs is a cause of cooling to those atmo- 
spheric strata near the earth, since the evaporation of lofty 
clouds and the consequent clearing of the sky must permit a 
freer radiation of the earth’s heat towards space, or at least 
into the higher regions of the atmosphere. And, as we have 
said, he considered this as a cause for the small amount of lunar 
warmth felt upon the earth. Mr. Park Harrison adopts this 
hypothesis to explain the high temperatures which he shows to 
occur at moon’s first quarter, and the low ones which happen 
near the last quarter ; and he considers that the time at which 
we observe the greatest effect in the former case is that when 
the part of the moon turned towards us has been least heated, 
and in the latter case that when the visible hemisphere has been 
longest subjected to insolation. 
We might expect to see traces of the clearing effect of the warm 
moon in tabulations of cloud registers according to lunar periods; 
but we do not find them. Professor Schiaperelli has arranged 
thirty-eight years’ cloud observations made at Vijevano in the or- 
der of days of lunation, and has laid down a series of curves which 
show the relations of clear and cloudy days to the moon’s age.f 
But he shows the sky to be clearest when Mr. Harrison’s theory 
requires that it should be cloudy, and cloudiest when, to fit the 
theory, it should be most clear. Meteorologists may one day 
reconcile these apparent anomalies. The evidence on either 
side is not, however, entitled to equal weight. Cloud observa- 
tions have not the same accuracy as those of temperature : 
there is no instrument wherewith to make them. Much 
depends upon the judgment of the observer, and much also 
upon what is understood by “ a cloudy night,” or any other 
verbal record, and much again upon the interpretation of 
numbers denoting proportions of sky-area covered with cloud. 
• “Phil. Tran*.,” l& r >8, p. 503. 
| “ Memoirs of the Lombardo’ Institute.” 3rd ser. Vol. i. Faac. iii. 
