1853] WRITINGS OF JOSEPH HENRY. 319 



tury was equally if not more fertile in the discovery of the 

 great principles of nature from which we are now reaping 

 so rich a harvest of practical results, but a knowledge of 

 these was not then so interwoven with the thoughts of the 

 common mind as to render them available for purposes of 

 art. Indeed the facts and elementary principles of science, 

 as well as the application of the rules which have been de- 

 duced from its higher generalizations, are now so familiar 

 that art has become vain of her attainments, has set herself 

 up as the architect of her own fortune, and disregards the 

 counsel of her more learned and sagacious sister. Such a 

 course however is usually accompanied with its own punish- 

 ment. The new edifices, designed by empiricism, are gen- 

 erally unstable structures, and most frequently involve the 

 ruin of the builder in their fall. 



It is true many valuable inventions have been founded on 

 the accidental discovery of simple facts; but such inventions 

 can never be perfected unless the principles of science on 

 which they are based are known. It is also true that many 

 arts may be successfully practiced by persons entirely igno- 

 rant of the principles of these arts. "We have a notable ex- 

 ample of this in the art of navigation, and in many of the 

 processes of engineering. The practical man in these cases 

 employs rules and deductions furnished by abstract science, 

 in the application of which he often becomes more expert 

 than the original author ; but sure progress in art cannot be 

 obtained without anterior or contemporaneous progress in 

 science. The inventor, to insure his success, must consult 

 the discoverer, and the practical skill of the one be directed 

 by the theoretical knowledge of the other. 



After what has been said in different parts of this address 

 it may be superfluous to give a formal definition of discov- 

 ery and invention ; but these terms are so frequently con- 

 founded with each other, and their misuse so much connected 

 with error, that it is necessary they should be clearly defined, 

 even at the risk of prolixity. 



By a discovery in science is understood the development of 

 a knowledge of the existence of some principle in nature not 



