282 EIGHTEENTH CENTURY. PT. ill. 



its formation. Meanwhile William Smith toiled over Eng- 

 land, mapping out the position of each rock as he saw it, and 

 thus he led the way to a long series of careful observations, 

 by which the whole geology of England has been worked 

 out. 



Chemistry. But the science which before all stands 

 forth in the eighteenth century is chemistry; for here the 

 discovery of the different gases led to certainty where all had 

 been guess-work before, showing the actual chemical changes 

 which are taking place on all sides in the world around us, 

 and teaching men to weigh and test invisible substances, and 

 not to rest satisfied with their knowledge of any substance till 

 they had traced it home to its first and simplest elements. We 

 need not recapitulate here the different discoveries of Scheele, 

 Bergmann, Black, Cavendish, Priestley, and Lavoisier. You 

 will remember how they all helped to overthrow the 

 imaginary theory of Phlogiston, and to prove that combus- 

 tion and respiration are merely chemical changes taking 

 place between different substances and the oxygen of our 

 atmosphere ; and this truth is the starting-point of modern 

 chemistry. 



Physics. Of Physics I have told you but little in this 

 century, but the two points we have considered have caused 

 greater changes throughout the world than any previous dis- 

 coveries. When Black proved the amount of heat which is 

 lying hid in water and in steam, and when Watt applied 

 it to the steam-engine, a giant power was born into the 

 world which has worked marvels. Visit any of the little 

 towns all over England and see the machines of all kinds 

 moved by the simple power of steam ; then go to the 

 great manufacturing towns and see the huge engines doing 

 the work of thousands of horses, with no other help than 



