894 Scientific Intelligence — Meteorology . 



rather than to the common order of things ? * — DarwirCs Journal 

 of a Voyage Round the World, part i., p. 132. 



5. Formation of Clouds. — In an article, vol. xxxviii., page 50 

 of this Journal, I endeavoured to shew that the phenomena of the 

 ascent of vapour, and its suspension in the region of the clouds, can- 

 not be accounted for by the agency of heat ; that the vapour in the 

 region of the clouds is at all times condensed ; and that " the forma- 

 tion of clouds is, in general, not owing to the sudden condensation of 

 the vapour, but to the escape of its electricity, thus allowing the par- 

 ticles to be brought nearer by the attraction of aggregation ; and a 

 still farther escape of the electricity enables such attraction to over- 

 come the electrical repulsion of the particles, and to form rain." 



The opinions advanced by Sir John Herschel (at the Cambridge 

 meeting of the British Association), on the effect of the heat of the 

 moon in dissipating clouds, tell against this theory ; and, although 

 the opinion of that eminent philosopher must have great weight, I 

 trust I may not be thought presumptuous in endeavouring to shew 

 that it cannot be the heat of the moon that causes the phenomenon 

 alluded to in the following extract. 



" Speaking of the climate of the moon, Sir J. Herschel considered 

 as possible the attainment of a very high temperature (far above 

 that of boiling water), by its surface, after exposure to unmitigated 

 and continual sunshine during nearly a whole fortnight. The moon, 

 therefore, when at the full, and for a few days after, must be, in some 

 small deorree, a source of heat to the earth ; but this heat, being of 

 the nature of culinary rather than of solar heat (as emanating from 

 a body below the temperature of ignition), will never reach the earth's 

 surface, being arrested and absorbed in the upper strata of an atmo- 

 sphere where its whole effects will necessarily be expended in the 

 conversion of visible cloud into transparent vapour. The phenome- 

 non of the rapid dissipation of clouds (in moderate weather) soon after 

 the appearance of the full moon (or of a moon so nearly full as to 

 appear round to the unassisted eye), which he stated himself to have 

 observed on so many occasions as to be fully convinced of the reality 

 of a strong tendency in that direction, seem to him explicable only 

 on this principle." — Athenaeum, July 19, p. 722. 



In the first place, it is very doubtful whether the moon does ab- 

 sorb heat sufficient to raise its temperature to such a degree : for as 

 the rays of a tropical sun are insufficient to melt the snow on the 

 higher mountains where the air is rarified, the fortnight's action of 

 the sun may have little influence on the surface of the moon, where, 

 according to the opinions of many, there is no atmosphere. 



Secondly, if the moon does absorb heat, and its temperature is 



* These droughts, to a certain degree, seem to be almost periodical. 

 1 was told the dates of several others, and the intervals were about fif- 

 teen years. 



