126 DEVELOPMENT AND PURPOSE CHAP. 



mately reduced to system by Ptolemy. Not that observa- 

 tion was neglected. On the contrary, in astronomy results 

 of great magnitude and, relatively to the instruments 

 available, of surprising accuracy were attained. The 

 catalogue of fixed stars made by Hipparchus was the best 

 available till the time of Tycho Brahe. The same observer 

 measured the length of the year within six minutes, dis- 

 covered the precession of the equinoxes and knew the 

 difference between the solar and the sidereal day. Indeed 

 it may be said that after the banishment from Athens of 

 Aristarchus for anticipating the Copernican theory the 

 theoretical development of astronomy was small as com- 

 pared with the advance in the description and accurate 

 measurement of the phenomena. Thus it would be true 

 to say that in astronomy the Greeks had laid the founda- 

 tions of that union of mathematical reasoning with exact 

 observation on which physical science depends. It would 

 also be true to say that in biology their observations, again 

 relatively to the available instruments, were searching and 

 valuable. On the other hand, it is clear that on this side 

 of knowledge in tracing the history of Greek enquiry we 

 are dealing only with beginnings. If observation is rich 

 in certain quarters of the field it is restricted to those 

 quarters, and generally lacks instruments of precision. 

 Direct experiment again is rare. Such an investigation as 

 that by which Ptolemy determined the angle of the refrac- 

 tion of light in passing from air to water, etc., is quite an 

 exceptional occurrence. Nor in spite of Archimedes at 

 Syracuse, or of the more regular and continuous labours 

 of Hero was the application of scientific principles a field 

 of general interest to the Greek enquirers. In short, their 

 body of recorded, organised, systematised experience was 

 relatively small, and most of it moreover was gained in 

 the later stages of their activity. It was in fact the natural 

 outcome of that elaboration of the conceptual order which 

 was the main work of their first and greatest period an 

 elaboration which laid the foundation alike of metaphysics, 

 of ethics and of mathematics. 



Now this work of conceptual construction is not a stage 

 which thought has passed through and left behind. It is 



