ON THE TtDES, ^ 577 



The second phenomenon is, that the tides are sensibly increased at the time 

 of the new and full moon; this increase and diminution constitute the spring 

 and neap tides; the augmentation becomes also still more observable when 

 the moon is in its perigee, or nearest the earth. The lowest as well as the 

 highest water is at the time of the spring tides; the neap tides neither rise so 

 high nor fall so low. 



The third phenomenon of the tides is the augmentation which occurs at the 

 time of the equinoxes: so that the greatest tides are when a new or full moou 

 happens near the equinox, while the moon is in its perigee. The effects of 

 these tides are often still more increased by the equinoctial winds, which 

 are sometimes so powerful as to produce a greater tide before or after the 

 equinox, than that which happens in the usual course, at the time of the 

 equinox itself. 



These simple facts are amply sufficient to establish the dependence of the 

 tides on the moon; they were first correctly explained by Newton as the 

 necessary consequences of the laws of gravitation, but the theory has been 

 still further improved by the labours of later mathematicians. The whole of 

 the investigations has been considered as the most difficult of all astronomical 

 problems ; some of the circumstances depend on causes which must probably 

 remain for ever unknown to us; and unless we could every where measure 

 the depth of the sea, it would be impossible to apply a theory, even if abso- 

 lutely perfect, to the solution of every difficulty that might occur. A very in- 

 judicious attempt has been made to refer the phenomena of the tides to causes 

 totally different from these, and depending on the annual melting of the 

 polar ice: the respectability of its author is the only claim Avhich it possesses 

 even to be mentioned; and a serious confutation of so groundless an opinion 

 would be perfectly superfluous. 



A detached portion of a fluid would naturally assume, by its mutual gra- 

 vitation, a spherical form, but if it gravitate towards another body at a 

 distance, it will become an oblong spheroid of which the axis will point to 

 the attracting body: for the difference of the attraction of this body on its 

 different parts will tend to separate them from each other in the greatest part 

 of the sphere, that is, at all places within the angular distance of 794-° froii^ 



