xi SOCIAL DEVELOPMENTS 213 



in the later Middle Age. But in the middle of the thir- 

 teenth century began a series of capital inventions which 

 prepared the way for a new epoch. Gunpowder (thirteenth 

 century) transforms the art of war. Printing from movable 

 blocks (fifteenth century) revolutionises knowledge. The 

 discovery of the microscope and telescope (early seven- 

 teenth century) opens up new worlds. The barometer 

 (seventeenth century) and the thermometer (1700) lay the 

 foundations of accurate measurement. There follows on 

 the industrial side the discovery of the smelting of iron 

 with coal (eighteenth century), and then comes the steam 

 engine and the great series of textile inventions which 

 created Lancashire and revolutionised England. These 

 inventions introduce us to a fourth stage in the relations 

 of man to nature. 



The discovery of the microscope and telescope reveal 

 new worlds, the development of mathematics a new instru- 

 ment, the systematic interrogation of experience a new 

 basis. We get below the surface properties of matter, and 

 appreciate and utilise the energies which they conceal. 

 Without seeking to determine the question of the ultimate 

 validity of the conceptions of physics, we may fairly assume 

 that they stand for a genuine advance in insight into the 

 real working of things, and that as the microscope gives us 

 genuine knowledge of a world beyond the ken of the 

 senses on which many of the most important events of 

 our lives depend, so similarly the conception of molecular 

 processes expresses a reality of which chemistry and physics 

 make use, and so, further, the ultra-molecular processes to 

 which the most recent science points, represent again, how- 

 ever inadequately, a further stage in the grasp of reality. 

 The characteristic of the industrial stage in which we live 

 is that industry, following science, goes below phenomena 

 and utilises the unseen forces of nature in engineering, 

 chemistry, medicine and hygiene for the purposes of man. 

 Industrially this stage is marked with some historical 

 definiteness as beginning towards the middle of the 

 eighteenth century. Some of the leading inventions which 

 made it possible go back, as has been shown, to the Middle 

 Ages and even to Greek science, but it was not till this 



