MOON AND BAROMETER. 



from the earth, and found that at perigee it was 29713, and at 

 apogee 29- 753. 



So far, therefore, as this small difference can be supposed to 

 indicate anything, it would indicate a prevalence to rain at 

 perigee and at apogee, which is in accordance with the observa- 

 tions of Schiibler. 



We have shown that the theory of the moon's attraction, 

 applied to explain atmospheric tides similar to those of the 

 ocean, would lead to the conclusion that the height of the baro- 

 meter observed at noon, when the moon is in her quarters, would 

 be less than its height at noon at new and full moon. Observa- 

 tion, however, shows the very reverse as a matter of fact. The 

 observation of M. Flaugergu6s gives the mean height of the 

 barometer at quadratures 29*756, and at new and full moon 

 29739 ; the height at quadratures being in excess to the amount 

 of 0'017. This result has been further confirmed by the more 

 recent observations of M. Bouvard, at the Paris Observatory ; 

 he has found the mean height of the barometer at the quarters 

 29786, and at new and full moon 29759 ; the excess at the 

 quarters being 0'027. 



4. Although, therefore, it cannot be denied that there exists a 

 certain relation between the barometric column and the lunar 

 phases, yet it is not the relation which the theory of atmospheric 

 tides would indicate ; and by whatever physical influence the effect 

 may be produced, it is certainly not the gravitation of the moon 

 affecting our atmosphere in a manner analogous to that by which 

 she affects the waters of the ocean. Any physical effects which 

 depend on the relative positions of the sun and moon, as seen 

 from the earth, would necessarily occur in the same order 

 throughout the year, when these two luminaries themselves 

 have corresponding positions in the heavens on the same days of 

 the year. 



At a very early period in the history of astronomical discovery, 

 it was known that, after the lapse of nineteen years, the sun 

 and moon assume on successive days of the year relative positions. 

 Thus, for example, if the moon were 90 behind the sun on a 

 certain day of a certain month in the year 1800, it would be 90 

 behind the sun on the same day of the same month in the year 

 1819, and again in the year 1838, and so on ; but on the same 

 day of the same month in any intermediate year it would have a 

 different relative position with respect to the sun. This cycle of 

 nineteen years was known to the Greeks, and was called the 

 Metonic cycle, from Meton, its reputed discoverer ; and it has 

 always been used as a convenient method of calculating eclipses 

 and other phenomena depending on the relative positions of the 



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