PHYSICAL METHOD. 505 



not have predicted, this constitutes a residual phenomenon, 

 requiring further study for the purpose of explanation; and we 

 must either search among the circumstances of the particular 

 case until we find one which, on the principles of our existing 

 theory, accounts for the unexplained phenomenon, or we must 

 turn hack, and seek the explanation hy an extension and im 

 provement of the theory itself. 



