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XIX. On a Cycle of Eighteen Years in the Mean Annual Height of the Barometer 

 in the Climate of London^ and on a constant variation of the Barometrical Mean 

 according to the Moon's Declination. By Luke Howard, Esq., F.R.S. 



Received February 4, — Read March 11, 1841. 



X HAVE already treated this subject, partially and in detail, in the ' Climate of 

 London*.* The further and full development of it in that way will be found an under- 

 taking more of labour than of diflSculty, the materials being already provided for doing 

 this through a lunar cycle of eighteen years ; but I am enabled, by means of these, 

 to present to the Royal Society some general results, which will prove interesting, 

 and probably important to the science to which they belong. 



The like method has been adopted in this paper as in my two former, read before 

 the Society, on the connexion of the barometric variation with the Lunar Phases and 

 Apsides. I have excluded, by appropriate averages, those effects of the lunar in- 

 fluence which belong not to the subject immediately before us. These, however, will 

 require, whensoever we may think it time to form a theory, to be examined conjointly 

 with the present and every other of the elements of this intricate subject. 



Table I. 



Barometrical Averages on successive Solar Years, from 1815 to 1832, constructed to 

 show the Moon's influence on the Mean Heights, varying according to her Decli- 

 nation : for the manner of forming which, see the remainder of this paper. 



* Vol. i. p. 172. 2nd Edition. 



