80 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



open end is an elastic band e, which prevents the messages from 

 falling out. When a carrier is placed in a tube and despatched, the 

 air fills up the loose end at /, and makes it fit the pipe quite close. 



The advantages of the pneumatic tube have been found so great, 

 that a system has been introduced into the large instrument gal- 

 lery for despatching messages from point to point for delivery and 

 retransmission. It has been found to work admirably, not only 

 economising time, but doing away with the constant rushing 

 about of messengers. 



In New York there has been constructed a short atmospheric rail- 

 way, leading from Warren Street to the lowest end of the city near 



IG. 50. The New York atmospheric railway. 



FIG. 51. The interior tube of a carriage. 



the North Paver. The cyclindrical tunnel has fixed on its lower 

 part (Fig. 50) two rails on which a vehicle for travellers alone runs ; 

 this is nearly of the same diameter as the tunnels through which it 

 passes, and is forced along by the pressure of the air. Fig. 51 repre- 

 sents the interior of this carriage. 



It will be seen, therefore, that these applications of atmospheric 

 pressure as a motive power are more than interesting experiments ; 

 their success in a small way is not difficult, but without improve- 

 ments not yet realised, they do not appear susceptible of being put 

 into practice on a large scale. 



