A HISTORY OF SCIENCE 



epoch to a convenient stopping-point, and then turn- 

 ing back to bring forward the story of another science. 

 Thus, for example, we tell the story of Copernicus and 

 Galileo, bringing the record of cosmical and mechanical 

 progress down to about the middle of the seventeenth 

 century, before turning back to take up the physio- 

 logical progress of the fifteenth and sixteenth centuries. 

 Once the latter stream is entered, however, we follow 

 it without interruption to the time of Harvey and his 

 contemporaries in the middle of the seventeenth cen- 

 tury, where we leave it to return to the field of mechan- 

 ics as exploited by the successors of Galileo, who were 

 also the predecessors and contemporaries of Newton. 



In general, it will aid the reader to recall that, so far 

 as possible, we hold always to the same sequences of 

 topical treatment of contemporary events; as a rule 

 we treat first the cosmical, then the physical, then the 

 biological sciences. The same order of treatment will 

 be held to in succeeding volumes. 



Several of the very greatest of scientific generaliza- 

 tions are developed in the period covered by the pres- 

 ent book: for example, the Copernican theory of the 

 solar system, the true doctrine of planetary motions, 

 the laws of motion, the theory of the circulation of the 

 blood, and the Newtonian theory of gravitation. The 

 labors of the investigators of the early decades of the 

 eighteenth century, terminating with Franklin's* dis- 

 covery of the nature of lightning and with the Lin- 

 naean classification of plants and animals, bring us to 

 the close of our second great epoch; or, to put it 

 otherwise, to the threshold of the modern period, 



