CHAPTER XII 



THE REIGN OF LAW DALTON, JOULE 



IN the middle of the eighteenth century, when 

 Lambert and Kant were recognizing system and 

 design in the heavens, little progress had been 

 made toward discovering the constitution of matter 

 or revealing the laws of the hidden motions of 

 things. Boyle had, indeed, made a beginning, not 

 only by his study of the elasticity of the air, but by 

 his distinction of the elements and compounds and his 

 definition of chemistry as the science of the composi- 

 tion of substances. How little had been accomplished, 

 however, is evident from the fact that in 1750 the 

 so-called elements earth, air, fire, water which 

 Bacon had marked for examination in 1620, were 

 still unanalyzed, and that no advance had been made 

 beyond his conception of the nature of heat, the ma- 

 jority, indeed, of the learned world holding that heat 

 is a substance (variously identified with sulphur, 

 carbon, or hydrogen) rather than a mode of motion. 



How scientific thought succeeded in bringing order 

 out of confusion and chaos in the subsequent one 

 hundred years, and especially at the beginning of the 

 nineteenth century, can well be illustrated by these 

 very matters, the study of combustion, of heat as a 

 form of energy, of the constituents of the atmosphere, 

 and of the chemistry of water and of the earth. 



Reference has already been made to Black's dis- 

 covery of carbonic acid, and of the phenomena which 



