184 Heredity. 



When in the works of one of the great philosophers, Aristotle, 

 Leibnitz, or Hegel, we read the scheme of some grand doctrine, 

 the argument, especially to a novice in such studies, is attractive 

 and convincing. The grandeur of the views, the breadth of the 

 method, the fruitfulness in results, are all alike charming. On 

 reflection some difficulties present themselves : these are the usual 

 processes of science, the inductions are legitimate, the deductions 

 exact, and yet we are dissatisfied some infirmity of mind hinders 

 an entire assent. The mind is undecided, hesitates between two 

 opinions. Yet, for the most part, no cause can be assigned for 

 this indecision, although the true reason is that to these doctrines 

 verification is wanting, which alone gives perfection to science and 

 produces an absolute conviction. When Aristotle reduces every- 

 thing in nature to the opposition between the possible and the 

 actual ; when Leibnitz reduces all to forces, and Hegel to the 

 evolution of ideas, their doctrine is irreproachable for logical 

 strength and precision. Yet we dare not assert that these doc- 

 trines are true, since verification is impossible. When, in the last 

 century, the doctrine of the pre-existence of germs in embryogeny 

 was taught, it was acceptable, was logically deduced, perhaps true. 

 Experiment alone could decide : and experiment showed it to be 

 false by proving epigenesis to be true; and this last theory has 

 been therefore adopted by science. 



Thus, of the three stages to be travelled, metaphysics traverse 

 the first two, the facts and the laws, but never reach the third, 

 strict verification by the differential method, and not that arbitrary 

 and hasty verification which explains some facts without concern 

 for those which it overlooks. Thus metaphysics remain beyond 

 and above verification, beyond and above science, confined for ever 

 to what is subjective. 



But, as has been already said, verification is but the first degree 

 in science. The second degree, that which completes the work, is 

 quantitative determination. That is the ideal to which all sciences 

 aspire, but to which but few attain. 



It is clear that, as the domain of quantity is that of number, 

 weight, and measure, every process from the qualitative to the 

 quantitative conducts us to more and more precise determinations. 

 But how does this transformation of quality into quantity take place, 

 and under what conditions ? 



