492 LOGIC OF THE MORAL SCIENCES. 



cumstances of a local or casual nature, such as the 

 configuration of the bottom of the ocean, the degree 

 of confinement from shores, the direction of the wind, 

 &c., influence, in many or in all places, the height and 

 time of the tide ; and a portion of these circumstances 

 being either not accurately knowable, not precisely 

 measurable, or at least not capable of being certainly 

 foreseen, the tide in known places commonly varies 

 from the calculated result of general principles by some 

 difference that we cannot explain, and in unknown 

 ones may vary from it by a difference that we are not 

 able to foresee or conjecture. Nevertheless, not only 

 is it certain that these variations depend upon causes, 

 and follow their causes by laws of unerring uniformity; 

 not only, therefore, is tidology a science, like meteor- 

 logy, but it is, what meteorology perhaps will never 

 be, a science largely available in practice. General 

 laws may be laid down respecting the tides, predictions 

 may be founded upon those laws, and the result will 

 in the main, though often not with complete accuracy, 

 correspond to the predictions. 



And this is what is or ought to be meant by those 

 who speak of sciences which are not exact sciences. 

 Astronomy w r as once a science, without being an 

 exact science. It could not become exact until not 

 only the general course of the planetary motions, but 

 the perturbations also, were accounted for, and referred 

 to their causes. It has now become an exact science, 

 because its phenomena have been brought under laws 

 comprehending the whole of the causes by which the 

 phenomena are influenced, whether in a great or only 

 in a trifling degree, whether in all or only in some 

 cases, and assigning to each of those causes the share 

 of effect which really belongs to it. But in tidology 

 the only laws as yet accurately ascertained, are those 



