182 GENERAL CONDITIONS OF SCIENTIFIC RESEARCH. 



at length become the most prevalent, if not the only race, 

 in the particular country in which it had originated. 1 His 

 theory was also in a slighter degree anticipated by some 

 observations made by Patrick Mathew in his book on 

 ' Timber for Ship Building, and the Cultivation of Trees,' 

 published in 1831. 



CHAPTEE XVIII. 



CHRONOLOGICAL ORDER OF DISCOVERY AND OF SCIENCE. 



In the discovery of truth, in the development of man's 

 mental power and privileges, each generation has its assigned 

 part; and it is for us to endeavour to perform our portion of 

 this perpetual task of our species. WHEWELL. 



As the possibility of making any particular discovery 

 depends upon the fact of certain other discoveries having 

 been previously made, it is evident that there exists a chro- 

 nological order of discovery, and that scientific research 

 cannot disclose those unknown truths which depend for 

 their birth upon our acquaintance with other truths not 

 yet known. It is evident also that the evolution of new 

 facts and laws is itself controlled by laws. After each 

 great discovery or series of discoveries has been made in a 

 particular subject, there usually occurs a lull in research in 

 that branch of science, chiefly because further advance in 

 that direction is prevented by our ignorance of other sub- 

 jects bearing upon it. 



1 Haeckel, History of Creation, vol. i. p. 150. 



