54 Wisconsin Academy of Sciences^ Arts, and Letters. 



tion, and then only because of this logical evolution and not 

 because of the operation of an innate organic force. Force, 

 whatever may be its genesis, is only the exertion of power, not 

 the increase of it. Exertion limits the view to the force im- 

 mediately in operation. We may replace one manifestation by 

 another, but the quantity is neither increased nor diminished 

 by this change. Change m form implies the operation of 

 force: and apart from such manifestation in matter, it escapes 

 the tests of science, and passes into the purely metaphysical 

 notion of cause. And unless the operation of force be con- 

 stant, or, if different forces are blended, variable according to 

 some determinate law, the action of which is constant and dis- 

 coverable, so that the different units of force are separately 

 measurable, the force thus irregular in its action can never be 

 placed in any scientific category. Evolution, then, cannot pro- 

 ceed from any innate organic impulse, unless the force that 

 tends to exact reproduction, and the force that induces a change 

 be equally and separately cognizable. Change must proceed 

 according to some law which accounts for the change, and dis- 

 tinguishes between the normal exertion of power and that ex- 

 ertion which causes a deviation. Science, to be science, must 

 explain apparent exceptions as fully as the regular operation 

 of forces, and that which causes the irregularity must be as dis- 

 tinctly cognizably by itself as the force which acts regularly. 

 Anything less than this is not science. The discovery of Nep- 

 tune was the result of the application of this principle; it was 

 a successful attempt to discriminate the force which caused va- 

 riation from the force which operated regularly. 



Each species represents the operation of certain vital forces, 

 and one cannot physically pass into another except by the in- 

 crease of this force, or at least by a change in the manner of 

 its manifestation ; and this increase in amount or this change 

 in direction must separately be accounted for. Nor does it 

 matter, for the purposes of this discussion, as to the genesis of 

 this added increment, further than to show that its origin must 



