4:2 NATURAL HISTORY 



to apply ; and tins, in the ever-varying forms of life, 

 can be done by no mechanical process ; it must be 

 by an effort of the mind, apprehending at the mo- 

 ment the entire combination of properties and rela- 

 tions. The first step in wrong theorizing is checked 

 by reference to the real thing, as the calculated dis- 

 tances and angles of the engineer are tested by 

 measurement of the base-line. It thus differs from 

 pure metaphysical investigations, by bringing into 

 constant action the perceptive faculties, as a check 

 to groundless speculations. While Mathematics 

 forces the mind along a given course by the iron 

 rail of necessity, in the relations of geometric 

 figures and algebraic symbols, Natural History 

 compels the mind to direct itself. It must here dis- 

 cover the track, before it can move, and keep itself 

 in place, not by the iron flanges of the car-wheel, 

 but by the quick eye and accurate balancing of the 

 equilibrist. While, then, it allows freedom of move- 

 ment, it demands accuracy, and corrects error by its 

 constant tests. It does not consist in the dreams of 

 any master's mind, who pities our want of rational 

 insight when we can not understand him,' or, under- 



