4- Dr. Thomson's Answer XJavs. 



into so fatal mistakes. Without the minutest attention to preci- 

 sion, chemical researches are not only useless, but pernicious. 

 The whole of chemistry, so far as it is entitled to the name of 

 science, consists in the accurate measurement of quantities ; and 

 all the progress which it ever has made, or ever will make, must 

 depend upon a rigorous and judicious use of the thermometer 

 and the balance. Indeed all science consists in the determina- 

 tion of quantity ; and the most eminent scientific men have not 

 been discoverers of new substances ; but have improved the 

 sciences to which they devoted themselves by a careful compa- 

 rison of the facts already known, deducing from them new 

 general laws, which had not been formerly recognised. Was it 

 not in this way that Newton acquired a rank in science to which 

 no other person has yet reached ? He added no new substance 

 to the list of those already known. He made no augmentation 

 in the number of planets, or of satelUtes, recognised before his 

 time. But he did what was far more difficult. He showed that 

 all the motions of the planetary bodies are the consequences of 

 certain simple general laws. By pointing out these he has 

 enabled his successors to determine the motions and the situa- 

 tions of all the planetary bodies for any period of time with the 

 minutest accuracy, and thus to bring the science of astronomy 

 in some measure to a state of perfection. 



Lavoisier existed at a period when chemistry was cultivated 

 in many parts of Europe with indefatigable zeal, and when new 

 substances and new properties of old bodies were made known 

 in considerable numbers almost every year. Lavoisier added no 

 elementary substance to those already known. It can scarcely 

 be said that he investigated the properties of a single chemical 

 body ; yet, assisted by the balance alone, he raised himself to a 

 higher chemical rank than any of his contemporaries. How 

 many new substances were discovered by Priestley, while 

 Cavendish scarcely added one to those already known? Yet 

 does not the latter rank much higher as a man of science than 

 the former ? To come to our own time, who has been a greater 

 benefactor to chemistry, or who has merited a higher reputa- 

 tion, or will stand better in the opinion of posterity, than Mr. 

 Dalton? Yet what new chemical element iias he discovered? 

 The discovery of new chemical bodies is undoubtedly a merito- 

 rious work, and the science is much indebted to those who have 

 had the good fortune to add to their number. But in the present 

 state of chemistry, it cannot be too forcibly inculcated, that he 

 who adds to the precision of the facts already known is of more 

 service to the science than he who adds to the number of ele- 

 mentary bodies. The science is still inundated by false facts, 

 which are retailed and appropriated by compiler after compiler 

 with the most careless mditference. Elementary books and 

 dictionaries of chemistry are annually accumulating, and errors 



