HUMAN NATURE A SUBJECT OF SCIENCE. 427 



in practice, since the data requisite for applying its principles 

 to particular instances would rarely be procurable. 



A case may be conceived, of an intermediate character 

 between the perfection of science, and this its extreme imper- 

 fection. It may happen that the greater causes, those on 

 which the principal part of the phenomena depends, are 

 within the reach of observation and measurement ; so that if 

 no other causes intervened, a complete explanation could be 

 given not only of the phenomenon in general, but of all the 

 variations and modifications which it admits of. But inas- 

 much as other, perhaps many other causes, separately insigni- 

 ficant in their effects, co-operate or conflict in many or in all 

 cases with those greater causes ; the effect, accordingly, pre- 

 sents more or less of aberration from what would be produced 

 by the greater causes alone. Now if these minor causes are 

 not so constantly accessible, or not accessible at all, to accu- 

 rate observation ; the principal mass of the effect may still, as 

 before, be accounted for, and even predicted ; but there will 

 be variations and modifications which we shall not be compe- 

 tent to explain thoroughly, and our predictions will not be 

 fulfilled accurately, but only approximately. 



It is thus, for example, with the theory of the tides. No 

 one doubts that Tidology (as Dr. Whewell proposes to call it) 

 is really a science. As much of the phenomena as depends on 

 the attraction of the sun and moon is completely understood, 

 and may in any, even unknown, part of the earth's surface, 

 be foretold with certainty ; and the far greater part of the 

 phenomena depends on those causes. But circumstances 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 circum- 

 stances being either not accurately knowable, not precisely 

 measurable, or 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 diffe- 

 rence that we are not able to foresee or conjecture. Neverthe- 



