vi INQUIRY AND INTERPRETATION 127 



Scientific observations of natural phenomena were 

 recorded four thousand years or more ago, but recogni- 

 tion of the essential importance of experimental science 

 of the modern type is only about three centuries old, 

 though the method was adumbrated at an earlier epoch. 



As an observer and a recorder Aristotle surveyed the 

 whole realm of Nature in his works, and had familiar 

 knowledge of a thousand varied forms of life. He 

 brought together an immense amount of accurate 

 observation and examined it with skilful reasoning, but 

 he was often led astray by pre-conceived ideas, and 

 based his conclusions upon reports which were more 

 curious than important. But he and other ancient 

 philosophers particularly lacked the scientific method of 

 inquiry by experiment. It is true that Pythagoras, in 

 the sixth century B.C., is credited with the use of mono- 

 chord, or single stretched string, of which the length and 

 tension can be varied, to determine by experiments the 

 law that the pitch of a note is inversely proportional to 

 the length of the vibrating string, and to discover 

 numerical relations between the various notes on the 

 musical scale. It is also true that Ptolemy, in the second 

 century A.D., determined by experiment the refraction 

 or amount of deviation which a beam of light undergoes, 

 from its original direction, when passing from air into 

 water, or into glass. But these determinations, with the 

 work in acoustics by Pythagoras, and Galen's proofs, by 

 the dissections of animals, of the relation between the 

 brain and the nerves, represent the sum total of experi- 

 mental research in Greek science. 



There was an interval of a thousand years between 

 Ptolemy's investigations in optics and the experiments 

 made by Alhazen, whose substantial studies of reflection, 

 refraction, vision, the human eye and related subjects 



