246 SCIENCE OF HOME AND COMMUNITY 



It was a long time after this, about 1700 years, before any 

 further thought was given to the principle of steam engines. 

 In 1629 an Italian named Branca described an engine which 

 was driven by steam driving directly against paddles on a 

 wheel, something like a water wheel. In 1663, a real steam 

 engine was built in England, which was actually made useful 

 in lifting water from the mines. About seventeen years 

 after this the first safety valve was invented. 



Newcomen's engine. In 1705 Thomas Newcomen con- 

 structed a steam engine that was a great improvement on 

 anything that had so far been made. It consisted of a 

 steam boiler and a cylinder in which moved a piston head. 

 The steam forced this head to one end of the cylinder, and 

 then, by turning a valve by hand, a spray of cold water was 

 led into the cylinder. This condensed the steam and formed 

 'a vacuum, and the atmospheric pressure forced the head 

 back. Thus the pressure of the steam forced the piston 

 head in one direction and the weight of the air forced it 

 back. This machine had to be watched and the valves turned 

 at the end of every stroke. It has sometimes been called 

 an atmospheric engine.- 



James Watt. The next great improvement was made by 

 James Watt during the latter half of the eighteenth century. 

 He invented a device by which the motion of the engine ad- 

 justed valves automatically in such a way that the steam 

 was taken in turn to each end of the cylinder, so that the 

 piston head was moved in both directions by steam pressure 

 instead of in only one direction as in the Newcomen engine. 

 The steam engine of to-day is essentially in principle the 

 same as the one invented by James Watt, except that there 

 is now being used for some purposes a different type of engine 

 called the turbine. But in the locomotive the Watt type of 

 engine is still used. 



First locomotive. The first locomotive was invented by 

 an Englishman named George Stephenson. In 1814 he 



