460 METEOROLOGY. 



resistauce. The results will be the less surprising when we recollect that 

 a cubic yard of air at the surface of the earth weighs about two pounds 

 avoirdupois, and that, cousequently, a stream of this fluid a quarter 

 of a mile long, moving with high velocity, must possess au immense 

 energy. 



EFFECT OF THE MOOX OX THE WEATHER. 



In answer to a letter on the subject. 



Since the form of the orbit of the earth is affected by the attraction 

 of Venus and the other planets, as well as by our satellite the moon, 

 they must in some degree also affect the form of the atmospheric cover- 

 ing of the globe, and tend to produce tides which are of greatest mag- 

 nitude when they are in opposition or conjunction with the sun : but 

 whether these disturbances of the atmosijhere or those produced by the 

 moon are of such a character as to give rise to the violent atmospheric 

 commotions denominated storms, is a question which has long agitated 

 the scientific world. 



The times and peculiarities of the meteorological occurrences are 

 more varied and less definitely remembered than almost any other 

 natural phenomena, and hence the large number of different rules for 

 predicting the changes of the weather. The only way of accurately 

 ascertaining the truth of any hyi^othesis in regard to atmospheric 

 changes, is that of having recourse to trustworthy records of the weather 

 through a long series of years, and it is one of our objects in collecting 

 meteorological statistics at the Smithsonian Institution to obtain the 

 means of proving or disijroving propositions of the character you have 

 advanced. 



The moon, being the nearest body to the earth, produces the highest 

 tide in the waters of the ocean, and must also produce the greater effect 

 on the aerial covering of the earth. It has, however, not been satisfac- 

 torily proved that the occurrence of the lunar tides is connected with 

 appreciable changes in the barometrical or thermometrical condition of 

 the atmosphere. The less pressure of the air, at a given place, ot 

 account of the action of the moon, is just balanced by the increased 

 height of the aerial column. 



The principal causes of the violent changes of the atmosphere 

 are, I think, due to its instability produced by the formation and con- 

 densation of vai)or. It is not imi)ossible, liowever, that when the air is 

 in a very unstable condition on account of the heat and moisture of the 

 lower strata, that the aerial tide may induce an overturning of the 

 tottering e(iuilibrium at some one place in the northern or southern 

 hemisplieie more unstable than the others, and thus commence a storm 

 which, but for this extraneous cause, would not have happened. To 

 detect, therefore, the influence of the moon, it wjU be necessary to com« 



