Masterpieces of Science 



Doubts were, however, expressed whether the 

 greater draught obtained by the contraction of 

 the blast-pipe was not counterbalanced in some 

 degree by the negative pressure upon the piston. 

 Hence a series of experiments was made with 

 pipes of different diameters, and their efficiency 

 was tested by the amount of vacuum that was 

 produced in the smoke-box. The degree of 

 rarefaction was determined by a glass tube fixed 

 to the bottom of the smoke-box and descending 

 into a bucket of water, the tube being open at 

 both ends. As the rarefaction took place, the 

 water would, of course, rise in the tube, and the 

 height to which it rose above the surface of the 

 water in the bucket was made the measure of the 

 amount of rarefaction. These experiments 

 proved that a considerable increase of draught 

 was obtained by the contraction of the orifice; 

 accordingly, the two blast-pipes opening from 

 the cylinders into either side of the "Rocket" 

 chimney, and turned up within it, were con- 

 tracted slightly below the area of the steam- 

 ports, and before the engine left the factory, the 

 water rose in the glass tube three inches above 

 the water in the bucket. 



The other arrangements of the " Rocket " were 

 briefly these: the boiler was cylindrical, with flat 

 ends, six feet in length, and three feet four inches 

 in diameter. The upper half of the boiler was 

 used as a reservoir for the steam, the lower half 

 being filled with water. Through the lower part 

 the copper tubes extended, being open to the 



