CHAP, vii.] V A I! 10 US TYPES OF STKAM-ENGINES. 433 



space between the two pistons and the socket c. Supported by the 

 convex surface of the piston, E', it pushes the concave surface of the 

 piston, E, and turns that piston and its axis in the direction marked 

 by the arrow. Since the two axes carry some cogs on the outside, 

 which make them turn in opposite directions, and with the same 

 velocity, the axis, c', and its piston move inside in the opposite 

 direction to the first. The second and third figures of 304 show the 

 position of the pieces after a quarter and half a revolution. At 

 this instant the piston, E, closes the opening B ; the steam can no 

 longer act on that piston, but it begins to act on the other. Be- 

 fore the commencement of the third quarter of the rotation (phase 4), 

 the opening of the exhaust port, D, is uncovered, the steam in the 

 space, a, escapes, the piston, E, is kept in motion by the other axis 

 and its acquired velocity, and so on for the rest. The steam thus 

 acts on each piston for a little more than half a turn, and each of the 

 axes receives its motion from the steam itself and the other axis 

 with which it is in connection ; one of these axes is the shaft of the 

 engine, the other has a fly-wheel. Behreris' rotatory engine is 

 obviously a steam-engine without expansion and without condensa- 

 tion ; though it is possible, by means of a suitably adjusted valve, to 

 make it work by expansion. 



We have already noted (p. 57, Book I.) one of the original appli- 

 cations of this engine, which consists in employing it to work a pump 

 constructed on the same principle and working in the same manner. 

 In the United States it is used in breweries and refineries as a force 

 pump for the various liquids, such as water, beer, syrup, &c. It is 

 little used in Europe, though it is obviously an engine of a certain 

 industrial importance. 



IV. THE POWER OF STEAM-ENGINES. 



SUCH is the. modern steam-engine as a whole, and in the principal 

 details of its structure. 



To -sum up in a few lines the description which has been the 

 object of the last three or four chapters, we see that the steam-engine 

 consists of: 



First, a boiler or steam-generator, which transforms into an 



7 F 



