634 Influence of the Moon on Atmospherical Phenomena. [Dec. 



It may be observed that (with one exception) the items of rain, 

 which fell with a low declination of the moon, in the two last months, 

 may be attributed to the effect of the conjunction and opposition of 

 the sun. Should this predominance of rain about the maximum de- 

 clination of the moon be found to obtain generally, it will account for 

 the third day before the new moon, and the 11th and 12th after, being 

 maxima — a circumstance which I noticed in my former paper, but was 

 unable to explain. The rainy-season lasts more or less from the 21st 

 June to the 21st September ? Now the day of new moon nearest the 

 21st June is nearly or actually the same with that of maximum north 

 declination. But as the sun leaves the northern tropic, the days of 

 maximum declination gradually separate from those of conjunction 

 and opposition, till by the time he is at the equator, they have reach- 

 ed the quarters. 



In adding up, therefore, the sums of rain which fell in successive 

 lunar revolutions, the chances were, that the third day before, and 11th 

 and 12th after, new moon, would be the maxima, as they were (upon 

 the whole) nearest to those of maximum declination of the moon. I 

 hope shortly to obtain a sight of the Nautical Almanacks for some 

 other years, and to have the honour of laying the results (whatever 

 they may be) of a comparision of them, with the registers, before the 

 Society. It only remains for me to explain, why I preferred compar- 

 ing the amounts of rain-fall, and the fluctuations of the dew-points 

 with the changes of the moon, to comparing the heights of the baro- 

 meter with the same, and as this latter plan has been suggested to me 

 from a highly esteemed quarter, I lose no time in replying. I first beg 

 to refer him to Daniell's Meteorological Essays, (1829), page 136, 

 and to assure him, that I agree with the observations there made, viz. 

 " That the total weight of the perpendicular column would not be af- 

 fected so much as that of its horizontal sections ; and the amount of 

 the lunar influence should be sought in the variations of the differences 

 of density between some high elevation and the level of the sea," &c. 

 For example, supposing a case where the aerial fluid was at rest 

 (the pressure being equal every where). Now, if any inequality were 

 to be caused (either by the presence of a luminary above the horizon 

 or otherwise) a current would instantly be set in motion to restore 

 the equilibrium, and any inequality, beyond what was necessary to 

 overcome the inertia of the air, would instantly be counteracted by an 

 increased velocity of current. But in estimating the rain-fail and 

 dew-points together, we get the sum of the effect produced — the accu- 

 mulated results of successive tides or currents. If we reflect what a 

 small difference of level is sufficient to set water in motion, we cannot 



