SCIENTIFIC INVESTIGATION 41 



here nothing but observation and experiment avail us. 

 The second is the determination of the constant relations 

 of the phenomena thus denned, and their expression in 

 rules or laws. The third is the explication of these par- 

 ticular laws by deduction from the most general laws of 

 matter and motion. The last two stages constitute Natu- 

 ral Philosophy in its original sense. In this region, the 

 invention of verifiable hypotheses is not only permis- 

 sible, but it is one of the conditions of progress. 



Historically, no branch of science has followed this 

 order of growth; but, from the dawn of exact knowledge 

 to the present day, observation, experiment, and specu- 

 lation have gone hand in hand; and, whenever science 

 has halted or strayed from the right path, it has been, 

 either because its votaries have been content with mere 

 unverified or un verifiable speculation (and this is the 

 commonest case, because observation and experiment are 

 hard work, while speculation is amusing) ; or it has 

 been, because the accumulation of details of observation 

 has for a time excluded speculation. 



The progress of physical science, since the revival of 

 learning, is largely due to the fact that men have gradu- 

 ally learned to lay aside the consideration of unverifiable 

 hypotheses; to guide observation and experiment by 

 verifiable hypotheses; and to consider the latter,- not as 

 ideal truths, the real entities of an intelligible world be- 

 hind phenomena, but as a symbolical language, by the 

 aid of which Nature can be interpreted in terms appre- 

 hensible by our intellects. And if physical science, dur- 

 ing the last fifty years, has attained dimensions beyond 

 all former precedent, and can exhibit achievements of 

 greater importance than any former such period can 

 show, it is because able men, animated by the true sci- 

 entific spirit, carefully trained in the method of science, 



