THE INJECTOR. 797 



force. Such a jet of steam is especially well adapted 

 for showing the phenomena of reaction and suction. 



A reaction apparatus moved by steam may be bad from the 

 dealers under the name ' Hero's engine,' or ' Eolipyle.' It consists 

 of a bollow spherical vessel, capable of rotating about an axis, 

 and fitted with two tubular appendages bent at right angles and 

 having narrow apertures, similar to those in fig. 144 (p. 201). By 

 immersing one of the apertures in water, and sucking at the other, 

 the vessel may be partly filled with water, which is then made to 

 boil by the application of a lamp. Very soon two jets of vapour 

 are forcibly discharged through the apertures, and on the principle 

 of reaction the globular vessel is driven round in an opposite 

 direction. 



A retort or flask is filled two-thirds with water, and closed by a 

 cork through which a glass tube passes. The end of the tube is 

 attached by means of an india-rubber tube to the horizontal tube of 

 the contrivance fig. 205 (p. 315). When the water is boiled over 

 a spirit-lamp the steam which issues produces a very powerful 

 suction, and dissipation of the liquid spray. 



The phenomena of suction may be rendered much 

 more striking by using the little contrivance repre- 

 sented in fig. 392, the principle of which is applied on 

 a large scale in the so-called ' injector/ which is a 

 steam-jet pump for feeding the boilers of steam-engines. 

 The steam issues from the small aperture of the tube 6, 

 the end of which reaches to within the narrow portion 

 of the tube c ; this part being, however, somewhat 

 wider than the point of the tube 5, so that the issuing 

 steam may expand and its density diminish. Through 

 c the steam passes out into the air, and at the same 

 time also some air from the space within the wider 

 tube a a, for as the density of the steam which issues 

 from b is diminished, air rushes from the space a a into 

 the narrow part of c, and is carried outwards by 

 the stearn. The air within a a becomes thus rarefied, 

 and if the tube d dips in water, the pressure of the 



