440 ARCHITECHNICS. 



pressure engines, at least in England, commenced with Messrs. Tre- 

 vithick and Vivian, in 1802 ; of which more will be said under Via- 

 tecture, in treating of locomotives ; and under Navitecture, in relation 

 to steamboats. The present water, wind, and steam power of Great 

 Britain, are estimated to perform the labor of more than twenty 

 millions of men. 



Our farther remarks on Machinery will be arranged under the heads 

 of Elements of Machinery ; Water power ; Wind, and Animal power ; 

 and Steam power. 



1. The Elements of Machinery, include, besides the simple me- 

 chanical powers, and the theory of forces, already referred to under 

 the branch of Mechanics, the various means of changing the direc- 

 tion and application of forces ; and the classification of machines. 

 Motion, in machinery, is either continuous, or alternate, that is alter- 

 nately in opposite directions. Continuous motion, on the earth's sur- 

 face, can only be circular, or curvilinear, unless by a succession of 

 matter, as in a running stream : but alternate or reciprocating motion 

 may be either curvilinear, or rectilinear, that is either in a curve, or 

 in a straight line. Rotary, or circular motion, is transmitted from 

 one axle to another, by band wheels, one of which is turned by the 

 friction of the band around them both ; or by rag wheels, having pro- 

 jections, and surrounded by a chain instead of a band ; or by cog 

 wheels, the teeth of which interlock; or by the perpetual screw, 

 acting on a cog wheel ; or by a universal joint, directly connecting 

 the axles ; or by double cranks, with two connecting rods, from the 

 cranks on one axle, to those on the other. The axle of large wheels 

 is often called the shaft; and when two unequal wheels gear 

 together, the smaller is sometimes called a pinion. 



Rotary motion may be made to produce alternate motion, by means 

 of cams, or eccentric and irregular wheels, pressing on levers ; and 

 especially by means of cranks. Rectilinear motion may be made to 

 produce circular, by acting on a circumference ; as in the rack, or 

 toothed bar, acting on a wheel ; or in the unwinding of a cord ; or in 

 the motion of windmills and water wheels. Alternate motion may 

 be changed from circular to rectilinear, or the reverse, by means of a 

 belt passing over a segment of a circle ; or by a vibrating crank and 

 connecting rod. Alternate motion may be converted into continuous, 

 by ratchet wheels, and catches ; or by scapements, as in clocks and 

 watches. The engaging and disengaging of machinery, is performed, 

 in the case of cogwheels, by moving one of them backward or 

 forward in the direction of the axle ; in band wheels, by having live 

 and dead pulleys, the latter turning separate from the axle ; and in 

 other cases, by means of attaching pins, or separable levers, or con- 

 necting rods. Machines may be classified, according to the kind of 

 power employed, as wind mills, hand mills, steam mills ; or accord- 

 ing to the nature of the process, as grist mills, saw mills, fulling 

 mills ; or according to the material operated upon, as flour mills, 

 sugar mills, and oil mills. On this subject we have no room to 

 dwell. 



2. Water Power, is generally applied by means of wheels, with 

 floats or buckets, in striking which, the water turns the wheel. 



