176 THE CHEMISTRY OF CREATION. 



part, the pressure of the superincumbent masses 

 of cool air, keeps the column up at its highest 

 point; and this we have called the "flow" of 

 the tide. 



With reference to the attraction of the moon 

 upon the air, it may be well to extract the 

 following sentences from the admirable address 

 of Sir E. H. Inglis, at the meeting of the 

 British Association, in 1847 : " The doctrine 

 of the influence of the moon and of the sun 

 on the tides was no sooner established, than it 

 became eminently probable, that an influence 

 exerted so strongly upon a fluid so heavy as 

 water, could not but have the lighter, and all 

 but imponderable fluid of air under its grasp. 

 It is now clear, as the result of the obser- 

 vations at St. Helena, by my friend, Colonel 

 Sabine, that as on the waters, so on the atmo- 

 sphere, there is a corresponding influence exerted 

 by the same causes. There are tides in the air 

 as in the sea ; the extent is, of course, deter- 

 rainable only by the most careful observations 

 with the most delicate instruments, since the 

 minuteness of the effect, both in itself, and in 

 comparison with the disturbances which are 

 occasioned in the equilibrium of the atmosphere 

 from other causes, must always present great 

 difficulty in the way of ascertaining the truth, 

 and had, in fact, till Colonel Sabine's researches, 



