528 LOGIC OF THE MORAL SCIENCES. 



As much of tlie phenomena as depends upon the attraction of the sun 

 and moon is completely understood, and may in any, even unknowTi, 

 part of the earth's surface, be foretold with certainty; and the far 

 greater part of the phenomena depends upon those causes. But cir- 

 cumstances of a local or casual nature, such as the configuration of the 

 bottom of the ocean, the degree of confinement from shores, the direc- 

 tion 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 com- 

 monly 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. Never- 

 theless, 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 meteorology, but it is, what 

 meteorology perhaps will never be, a science largely available in 

 practice. General laws may be laid down respecting the tides, pre- 

 dictions may be founded upon those laws, and the result will in the 

 main, though often not \nth 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 Avas 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 refeiTed to their causes. It has now be- 

 come 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 de,gi"ee, 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 of the causes which affect the 

 phenomenon in all cases, and in a considerable degree ; while others 

 which affect it in some cases only, or, if in all, only in a slight degree, 

 have not yet been sufficiently ascertained and studied to enable us to 

 lay doMTi their laws ; still less to deduce the completed law of the phe- 

 nomenon, by compounding the effects of the greater with those of the 

 minor causes. Tidology, therefore, is not yet an exact science ; not 

 from any inherent incapacity of being so, but from the difficulty of 

 ascertaining with complete precision the real derivative uniformities. 

 By combining, however, the exact laws of the greater causes, and of 

 such of the minor ones as are sufficiently known, with such empirical 

 laws or such approximate generalizations respecting the miscellaneous 

 variations as can be obtained by specific observation, we can lay down 

 general propositions which will be true in the main, and upon which, 

 with allowance for the degree of their probable inaccuracy, we may 

 safely gi-ound om- expectations and om- conduct. 



§ 2. The science of human nature is of this description. It falls far 

 short of the standard of exactness now realized in Astronomy; but 

 there is no reason that it should not be as much a science as Tidology 

 is, or as Astronomy was when its calculations had only mastered the 

 main phenomena, but not the perturbations. 



