THE MOON AND THE WEATHEE. 379 



But such observations have not been carried to the necessary extent. If the ques- 

 tion of fact were, whether there be any obvious and glaring correspondence of 

 periodicity between the lunar phases and the atmospheric vicissitudes, 'it would 

 be instantly answered in the negative. For although we do not possess sufficient- 

 ly accurate and long-continued series of observations to decide the question wheth- 

 er the moon has any atmospheric influence, however small, we possess a sufficient 

 bcdy of ascertained facts to justify the conclusion that her influence is certain- 

 ly not considerable, and that, whatever be its amount, it is probably in a great 

 degree obliterated by the vast number of modifying and disturbing causes 

 which are constantly in action. 



Let us consider for a moment the theoretical question. If the moon can act 

 upon our atmosphere by attraction, as she acts upon the waters of the ocean, 

 she will produce atmospheric tides, similar to those of the waters. The great- 

 er mobility of air will cause those tides to be formed more rapidly than the 

 water tides ; and it may be, perhaps, assumed that the tides of the atmosphere 

 will always be placed, either exactly, or very nearly under the moon. Thus, 

 is there is high water twice daily, so would there be high air twice daily ; and 

 'he times of this air tide would correspond with the moments of the transit of 

 lie moon over the meridian above and below the horizon. , 



The same causes, also, which at new and full moon, produce spring tides, 

 wid at the quarters, neap tides, would produce spring and neap atmospheric 

 '.ides at the same epochs. At new and full moon, therefore, the air ought to 

 be higher, daily, at noon and midnight than at any other times during the 

 month ; and, on the other hand, at the quarters it ought to be lower. 



If, then, the barometer be observed twice daily, viz., at the times of 

 the moon's transit over the meridian, above and below the horizon, it ought 

 (so far as it will be affected by the sun and moon) to be the highest at new 

 and full moon, and lowest at the quarters. Now as the rise of the barometer 

 generally indicates fair weather, and its fall foul weather, the conclusion to 

 which this would lead, would be, that the epochs of new and full moon should 

 be generally fair, while at the quarters bad weather would generally prevail. 

 This, however, is not the popular opinion. The traditional maxim is that a 

 change may be looked for at new and full moon ; that is, if the weather be 

 previously fair, it will become foul ; if previously foul, fair. 



M. Arago has made an ingenious attempt at the evaluation of the very mi- 

 nute effect of what we have called atmospheric tides. To comprehend his rea- 

 soning it will only be necessary to consider that, at a new and full moon, 

 the sun and moon pass the meridian above and below the horizon together ; 

 and therefore, that high air, or atmospheric tides, must at these times take place 

 at noon and midnight ; low air would therefore occur about six, A. M., and six. 

 P. M. Thus so far as the attraction of the moon affects the atmosphere, the 

 barometer, which rises and falls as the atmosphere rises and falls, would be 

 affected by an ascending movement for six hours before noon and midnight, 

 I and for six hours after these times. But, when the moon is in the quarters, 

 ) being then one fourth of the heavens removed, before or behind the sun, it will 

 J pass the meridian, whether above or below the horizon, about six hours later 

 1 or earlier than the sun. At the quarters, therefore, the atmospheric tides would 

 J occur about six, A. M., and six, P. M. Thus at the quarters the barometric 

 ' column, so far as it is influenced by the moon's attraction, would be affected 

 ! with a descending motion for about six hours after these times. It will be ev- 

 | ident, that if we were in a condition to estimate the amount of these baromet- 

 ! ric movements, we should be at once in a condition to declare the amount of 

 ' the lunar attraction on our atmosphere. 



But these effects, if appreciable at all, are modified by at least one other in- 



