292 



March 11, 1841. 



Sir JOHN WILLIAM LUBBOCK, Bart., V.P. and Treasurer, 

 in the Chair. 



The following papers were read : 



1. " On a Cycle of Eighteen Years in the Mean Annual Height of 

 the Barometer in the Climate of London ; and on a Constant Varia- 

 tion of the Barometrical Mean, according to the Moon's Declina- 

 tion." By Luke Howard, Esq., F.R.S. 



For obtaining the general results communicated in the present 

 paper, the author has followed the same method as that he had 

 adopted in the two former papers laid before the Society on the con- 

 nexion of the barometrical variation wdth the lunar phases and apsides. 

 Tables are given of the barometrical averages on successive solar 

 years, from 1815 to 1832, so constructed as to exhibit the variation 

 of the moon's influence according to her declination ; and also of 

 these averages on successive cycles of nine solar years, classed 

 according to the moon's place in declination, on either side of the 

 equator. The results deduced from these comparisons are, first, 

 that the barometrical mean in this climate is depressed by the moon's 

 declination being to the south of the equator ; and, secondly, that 

 this depression takes place gradually, commencing with the moon's 

 being in full north declination, and proceeding through her remain- 

 ing positions to the time when she crosses the equator to resume the 

 northern declination; at which season, the whole pressure that had 

 been withdrawn from the atmosphere is suddenly restored. The 

 author thinks there is evidence of a great tidal wave, or swell in the 

 atmosphere, caused by the moon's attraction, preceding her in her 

 approach to, and following her slowly as she recedes from these la- 

 titudes ; so that were the atmosphere a calm fluid ocean of air, of 

 uniform temperature, this tide would be manifested with as great re- 

 gularity as those of the ocean of waters. But the currents uniformly 

 kept up by the sun's varying influence effectually prevent this from 

 taking place, and involve the problem in complexity. He finds that 

 there is also manifested in the lunar influence a gradation of effect, 

 which operates through a cycle of eighteen years. The mean pres- 

 sure of the atmosphere during the first part of this period increases ; 

 and then, after preserving for a year its maximum amount, again 

 decreases through the remaining years of the cycle, but exhibits, 

 towards its minimum, some fluctuations before it again regularly 

 increases. 



2. " On a remarkable depression of the Barometer in November 

 1840, agreeing very closely in its movements and results with that 

 of December 1821." By Luke Howard, Esq., F.R.S. 



The object of the author in the present paper is to show the close 

 correspondence of the extraordinary depression of the barometer in 

 the months of October and November of last year (1840), and of 

 the remarkably stormy weather which prevailed at the same period. 



