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Mr. P. E. Chase on Aerial Tides. [June 16, 



exert a very important influence on the atmospheric and magnetic currents, 

 the deposition of moisture, and other meteorological phenomena. As the 

 height of the wave varies with the changing phases of the moon*, its effects 

 must likewise vary in accordance with mathematical laws, the proper study 

 of which must evidently form an important branch of meteorological science. 



Besides this daily wave, there appears to be a much larger, but hitherto 

 undetected, weekly wave. Itl. Flangerguesf, an astronomer at Viviers in 

 France, extended his researches through a whole lunar cycle, from Oct. 1 [), 

 1808 to Oct. 18, 1827, and he inferred from his observations — 



1 . That in a synodical revolution of the moon, the barometer rises regu- 

 larly from the second octant, when it is the lowest, to the second quadra- 

 ture, when it is the highest, and then descends to the second octant. 



2. That the varying declination of the moon modifies her influence, the 

 barometer being higher in the northern lunistice than in the southern. 



The more recent and more complete observations at St. Helena give 

 Somewhat different results, which serve to confirm the natural a priori con- 

 viction that there are two maxima and two minima in each month. The 

 means of three years' hourly observations, indicate the existence of waves 

 which produce in the first quarter a barometric effect of + '004 in., in the 

 second quarter of — 'OlGin., in the third quarter of +'018 in., and in the 

 fourth quarter of —'006 in. — results which appear to be precisely ac- 

 cordant, in their general features, with those which would be naturally anti- 

 cipated from the combination of the cumulative action of the moon's at- 

 traction, with the daily wave of rotation, and the resistance of the aether. 



One peculiarity of the lunar-aerial wave deserves attention, for the indi- 

 rect confirmation that it lends to the rotation theory of the aerobaric tides, 

 and the evidence it furnishes of opposite tidal effects, which require con- 

 sideration in all investigations of this character. When the daily lunar 

 tides are highest, their pressure is greatest, the lunar influence accumulating 

 the air directly under the meridian, so as to more than compensate for the 

 diminished weight consequent upon its ''lift." But in the general aerial 

 fluctuations, as we have seen heretofore, and also in the weekly tides which 

 we are now considering, a high wave is shown by a low barometer, and vice 

 versa. The daily blending of heavy and light waves produces oscillations 

 which are indicated by the alternate rise and fall of the barometer and ther- 

 mometer at intervals of two or three days. 



M. Flangergues's observations at perigee and apogee seem to show that 

 a portion of the movement of the air by the moon is a true lift, which, like 

 the lift of rotation, must probably exert an influence on the barometer. 

 On comparing the daily averages at each of the quadratures and syzygies, 

 I found the difference of temperature too slight to warrant any satisfactory 

 inference, but a similar comparison of the hourly averages, at hours when 



* The height at St. Helena appears to fluctuate between about '9 and 1-6 ft. 

 t Bib. Univ., Dec. 1827. 



