WEATHER PROGNOSTICS. 



sun and moon. In a solar eclipse, the sun and moon must 

 occupy nearly the same position in the heavens ; and in a lunar 

 eclipse, nearly opposite positions : it is evident, therefore, that if 

 an eclipse occur on any day in any given year, an eclipse of the 

 same kind must occur on the corresponding day in every nine- 

 teenth succeeding year. The tides, depending as they do on the 

 relative positions of the sun and moon, would be calculated with 

 facility by means of the same cycle ; and meteorologists who 

 hold the doctrine that atmospheric vicissitudes depend solely or 

 chiefly upon the relative aspects of the sun and moon, have 

 favoured the doctrines, that there is a general cycle of weather, 

 the period of which corresponds with that which we have 

 noticed. Thus they hold, that the general changes of weather 

 succeed each other in the same, or almost the same order, 

 throughout every successive period of nineteen years. 



We shall not here object, on theoretical grounds, to the 

 doctrine that the true amount of the Metonic cycle is not 

 precisely nineteen years. But it is subject to a stronger 

 objection, founded on the principles which its supporters them- 

 selves rely upon. The attraction of bodies in virtue of their 

 gravitation increases in the same proportion as the square of the 

 distance diminishes ; and as we have already stated that the 

 moon's distance from the earth is variable to an extent not 

 inconsiderable, it is evident that her influence on the atmosphere 

 ought to be expected to depend much more on that variation of 

 distance, than on her relative position with respect to the sun. 

 Now, although the cycle of nineteen years corresponds with the 

 changes of her relative position to the sun as seen from the earth, 

 yet it has no correspondence whatever with the variation of her 

 distance ; and although, on each day of each succeeding period 

 of nineteen years, she will have the same apparent position 

 relatively to the sun, she will not have the same distance from 

 the earth, and, therefore, will not exert the same attraction on 

 our atmosphere. M. Arago (to whom we are indebted for 

 the most complete investigation of this question, and for the 

 collection of the labours of others upon it) has successfully 

 shown that observation affords no countenance or confirmation 

 whatever to this hypothesis. 



The variation of the moon's distances from the earth (to which 

 we have more than once adverted) is occasioned by the fact that 

 her path round the earth is not circular, but oval the position 

 of the earth being nearer to the one end than the other. As the 

 moon, therefore, approaches the furthermost extremity of her 

 oval orbit, her distance from the earth continually increases until, 

 arriving at that point, it becomes greatest ; as she moves from 

 78 



