6 THE REALITIES OF MODERN SCIENCE 



difficulties of language. At this time in the develop- 

 ment of man he was just learning to talk. His few 

 ideas and fewer words were concerned with concrete 

 objects such as water, fire, food, sun, and moon or with 

 his own sensations such as cold, hunger, and fatigue. 

 He had no vocabulary for expressing abstract ideas. 

 Imagine the difficulty of trying to tell a primitive man 

 of the speed record of an automobile, of the efficiency 

 of its engine, or of the refinement of its lines and up- 

 holstery. 



Between the discovery of the method of conserving 

 fire and its production by a simple machine many 

 thousands of years must have intervened. A primitive 

 method is that of rubbing a sharp stick back and forth 

 in a groove cut in a block of hard wood. For this 

 concrete case he had learned that his work in rubbing 

 together two surfaces resulted in heat. The heat 

 produced by his efforts did not diffuse rapidly and so 

 make the entire block of wood a little warmer than it 

 was before. Instead it was concentrated in the wood 

 adjacent to the groove. If he rubbed hard enough, 

 that is, if he did enough work, this part of the block 

 would then rise rapidly in temperature, smoke, and 

 finally set fire to dry wood dust or other trader placed 

 in the groove. 



This simple device is not, however, a machine. It 

 is merely a special tool for rubbing and a block to be 

 rubbed. When primitive men arranged a combination 

 where the rubbing tool was actuated by another part 

 of the device, which part in turn was controlled by the 

 operator, then he had a machine. In Fig. 1 is shown 

 such a fire-making machine. It is of course a develop- 



