580 SPECIAL METHODS OF DISCOVERY. 



conditions as to fit them to those conditions and to the 

 work to be done. It was partly by comparison of bones 

 that Cuvier discovered that each organised being formed 

 a complete system in itself, and that from a knowledge 

 of one part of a skeleton the construction and form of 

 the entire remainder might be inferred. It was by com- 

 parison of facts with the doctrine of homology that 

 Greoffroy St. Hilaire discovered that the essential parts of 

 all vertebrate animals are the same, with modifications 

 only suited to their particular requirements. He dis- 

 covered that nature 'had formed all living beings on 

 one general plan,' varied only in minor parts similar 

 parts being modified so as to fulfil different functions in 

 different animals. It was by means of comparison of a 

 multitude of well-known facts that Darwin inferred and 

 discovered his Theory or Doctrine of Descent in the living 

 world of plants and animals. It was by viewing them as 

 affected by the two chief principles of Inheritance and 

 Adaptation, and with the aid of comparison, he evolved 

 his theory; he supported by facts what Lamarck sug- 

 gested as an hypothesis, and suggested the probable causes. 

 Dalton's theory, also, of the rule of multiple proportions 

 in chemistry, in accordance with his theory of atoms, was 

 suggested by his examination of olefiant and carburetted 

 hydrogen gases; he discovered it by comparing known 

 facts with an hypothesis he had imagined ; and he did 

 this at a time when circumstances had become sufficiently 

 ripe for the purpose, i.e., when knowledge of chemical 

 facts had become sufficiently extensive. 



c. By comparing facts, and collecting together 

 similar ones. Discovery by simple generalisation is very 

 common, and is the method by which we have acquired a 

 knowledge of the existence of different groups of bodies, 

 forces, properties, actions, and phenomena such as solids, 



