Chase, I -j<U [April :il, 



nation imposes no restraint on the universe ; it is only a confession of our 

 own sliortsightedness. He wlio sees the necessity of a Wise, Everlasting 

 and Almighty Omnipresence, also sees that the present order of things 

 must continue as long as its Ruler wills. lie who sees that the Omnipres- 

 ent Power acts "in ways which may be represented by harmonic or cycli- 

 cal undulations in an elastic medium," also sees that more is implied in 

 the equality of elastic action and reaction than has yet been fathomed by 

 the sounding line of the most skillful analysis. 



215. Tides. 



The danger of hasty generalizations from investigations which are neces- 

 sarily of a partial character, is well illustrated by the various speculations 

 which have been set forth about tidal action. The equilibrium-hypothesis and 

 each of the dyjiamic hypotheses have severally considered important rela- 

 tions and interactions between the disturbed and disturbing bodies, but the 

 incompleteness of them all is shown by our inability yet to explain some 

 of the phenomena which are of, daily occurrence, as well as by our com- 

 plete ignorance as to the normal position of the tidal crests. Bernouilli, and 

 Laplace for certain mean depths of ocean, assumed that it should be high 

 water under the moon ; Laplace for other depths, Delaunay and Airy 

 have given satisfactory evidences of tendencies to high tide when the moon 

 is in the horizon ; sailors have a prevalent belief that the high water, in 

 mid-ocean, lags about three hours behind the moon; many mathematicians 

 think that either friction or inertia may produce such lagging, but it has 

 never been shown that there is any tidal friction, or that inertia 

 can delay any normal tidal action. Some of the most satisfactory 

 results have been reached through considerations of the elasticity 

 which is involved in wave-propagation, but the inter-molecular elasticity, 

 the extent to which the several particles of water are free to fall towards 

 or recede from the attracting body, and the variations of weight conse- 

 quent on variations of gravitating tendency, have not been sufficiently 

 studied. 



216. Barometric Analogy. 



Fortunately, upon at least one of the foregoing points, we can ask nature 

 a simple question, to which she gives a satisfactory answ^er. Is there any 

 evidence of tidal disturbance of weight? Yes, in the daily fluctuations of 

 the barometer. They are certainly tidal, even if we fail to see in them any 

 likeness to the ocean tides. The air, which is heated and expanded by the 

 sun's rays, is carried forward by the earth, in its orbital revolution and 

 daily rotation, with a continual tendency of each particle to maintain the 

 instantaneous direction of its motion. This tendency is represented, not 

 by the simple momentum of the particles, but hy their vis viva, and is ac- 

 companied by gravitating tendencies, which are sometimes antagonistic 

 and sometimes co-operative, towards the earth and towards the sun. 

 Tl^eir own elasticity concurs with the elasticity of any intervening me- 



