428 LOGIC OF THE MORAL SCIENCES. 



less, not only is it certain that these variations depend on 

 causes, and follow their causes by laws of unerring uniformity ; 

 not only, therefore, is tidology a science, like meteorology, 

 but it is, what hitherto at least meteorology is not, a science 

 largely available in practice. General laws may be laid down 

 respecting the tides, predictions may be founded on those laws, 

 and the result will in the main, though often not with com- 

 plete 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 

 was 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 become an exact 

 science, because its phenomena have been brought under laws 

 comprehending the whole of the causes by which the pheno- 

 mena 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 the theory of the tides the only laws as yet accu- 

 rately 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 been sufficiently ascertained and 

 studied to enable us to lay down their laws ; still less to deduce 

 the completed law of the phenomenon, 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 on which, with allowance for the 

 degree of their probable inaccuracy, we may safely ground our 

 expectations and our conduct. 



