METEOROLOGY.. 51 



effect of the sun''s heat would only he to produce daily fluctuations of 

 temperature, and the changes of the seasons. 



5. Next let us suppose the moon also to act upon the atmosphere. 

 Its action cannot be one of calorific influence, by which a general lunar 

 circulating system is produced like that produced by the sun. It is 

 one purely of attraction. It can only exert a modilying influence up- 

 on the results of the solar action — its effects are only of a minor nature 

 superinduced upon those of the sun. 



If the moon did not exert a strong attraction upon the atmosphere 

 and thereby disturb its condition, the laws of nature would be subject 

 to a strange irregularity. We would Witness the singular fact of a very 

 marked influence exerted upon the more distant, the heavier, and the 

 less movable waters of the ocean, producing tides of considerable mag- 

 nitude ; and at the same time no effect produced on the nearer, the light- 

 er, and the extremely movable mass of the atmosph-ere. Such a sup- 

 position is unphilosophical and absurd. There must, froin the necessity 

 of the case, be both solar and lunar tides in the atmosphere, of which 

 the latter must, however, be by far the greater. It is indeed true that 

 these tides are not easily recognized by any difference of pressure pro- 

 duced at the earth''s surface, as might at first view be expected. But then 

 it must be remembered that the solar heat exerts such an all-controlling 

 power in producing changes of pressure, currents and counter-currents, 

 as almost to conceal the lunar tides, if there be any. These, being mixed 

 up with the more powerful movements due to changes of temperature, 

 can do no more than modify or change in a subordinate degree the con- 

 dition of the atmosphere as influenced by the solar heat. It is these 

 modifications or superinduced clianges which give its existing character 

 to the weather. 



That these changes should not occur at the precise time at which 

 the moon reaches any particular position is to be expected, since even 

 the tides of the ocean follow at some distance the moon in its diurnal 

 course j and that they should be influenced by local circumstances is 

 likewise to be expected, since the latter are also influenced and modified, 

 and sometimes even entirely destroyed by the situation and outline of 

 sea coast. This is a sufficient answer to the first objection above stated. 

 •The second objection is answered by a consideration of the fact, that, 

 as the lunar action is but a modifying influence, inducing upon the great 

 circulating system produced by the sun, certain minor changes, these 

 changes must be carried forward in that general circulation. If, there- 

 fore, a rliange is produced by the moon in the region of the trades, or of 

 its own declination, by which cloud and rain are produced, that change 



