VAPOUR JETS. 



is in contact with the finger cannot give up 

 much heat to the skin. 



Secondly, this true steam has also, like 

 gases, very little power of conducting heat, so 

 that the film next the skin cannot carry to it 

 the heat from the adjoining layers of steam. 



When to these considerations we add the 

 fact that the outer layer of skin, which is not 

 sensitive, has to be heated by the small amount 

 of heat imparted, before the deeper and sen- 

 sitive layers can receive much heat, we see 

 how it is possible to expose the skin to steam- 

 heat for a short time. 



But it must be for a short time only. If 

 the experimenter displays too much coolness 

 and deliberation, heat enough will be conveyed 

 before long to burn, though not to scald, the 

 skin. 



2. The Stronger Overcome by the Weaker. 



At the time of its invention the steam 

 injector was one of the most surprising of 

 engineering contrivances. Few people, not en- 

 gineers, know what an injector is or does ; but 

 it is well worth considering. 



From a steam boiler comes a steam pipe, 

 supplying the engine with steam. From the 

 steam pipe comes a branch which takes steam 

 to the injector. In the injector the current of 

 steam meets a current of water brought by 



