602 



MACHINERY. 



gained by their use, however combined. Whatever 

 force is applied at one part, can only be exerted at 

 some other, diminished by friction and other incidental 

 causes ; and whatever is gained in the rapidity of 

 execution, is compensated by the necessity of exert- 

 ing additional force. These two principles should 

 be constantly borne in mind, and teach us to limit 

 our attempts to tilings which are possible. See 

 Hydraulics, Hydrostatics, Mechanics, Steam. 



1. Accumulating Power. W lien the work to be done 

 requires more force for its execution than can be 

 generated in the time necessary for its completion, 

 recourse must be had to some mechanical method of 

 preserving and condensing a part of the power exerted 

 previously to the commencement of the process. 

 This is most frequently accomplished by a fly-wheel, 

 which is a wheel having a iieavy rim, so that the 

 greater part of the weight is near the circumference. 

 It requires great power, applied for some time, to set 

 this in rapid motion, and, when moving with con- 

 siderable velocity, if its force is concentrated on a 

 point, its effects are exceedingly powerful. Another 

 method of accumulating power consists in raising a 

 weight, and then allowing it to fall. A man, with a 

 heavy hammer, may strike repeated blows on the 

 head of a pile without any effect; but a heavy weight, 

 raised by machinery to a greater height, though the 

 blow is less frequently repeated, produces the desired 

 effect. 



2. Regulating Power. Uniformity and steadiness 

 in the motion of the machinery are essential both to 

 its success and its duration. The governor, in the 

 steam-engine, is a contrivance for this purpose. A 

 vane or fly of little weight, but large surface, is also 

 used. It revolves rapidly, and soon acquires a 

 uniform rate, which it cannot much exceed ; because 

 any addition to its velocity produces a greater addi- 

 tion to the resistance of the air. This kind of fly is 

 generally used in small pieces of mechanism, and, 

 unlike the heavy fly, it serves to destroy, instead of 

 to preserve, force. 



3. Increase of Velocity. Operations requiring a 

 trifling exertion of force may become fatiguing by 

 the rapidity of motion necessary, or a degree of rapi- 

 dity may be desirable beyond the power of muscular 

 action. Whenever the work itself is light, it becomes 

 necessary to increase the velocity in order to econo- 

 mize time. Thus twisting the fibres of wool by the 

 fingers would be a most tedious operation. In the 

 common spinning-wheel, the velocity of the foot is 

 moderate, but, by a simple contrivance, that of the 

 thread is most rapid. A band, passing round a large 

 wheel, and then round a small spindle, effects this 

 change. This contrivance is a common one in ma 

 chinery. 



4. Diminution of Velocity. This is commonly 

 required for the purpose of overcoming great resist- 

 ances with small power. Systems of pulleys afforc 

 an example of this: in the smoke-jack, a greater 

 velocity is produced than is required, and it is there 

 fore moderated by transmission through a number o: 

 wheels. 



5. Spreading the Action of a Force exerted for a 

 few minutes over a large Time. This is one of the 



most common and useful employments of machinery 

 The half minute which we spend daily in winding 

 up our watches is an exertion of force which, by the 

 aid of a few wheels, is spread over twenty-four hours 

 A great number of automata, moved by springs, may 

 be classed under this division. 



6. Saving Time in natural Operations. The pro 

 cess of tanning consists in combining the tanning 

 principle with every particle of the skin, which, b; 

 the ordinary process of soaking it in a solution of the 

 tanning matter, requires from six months to tw 



ears. By enclosing the solution, with the hide, in 

 close vessel, and exhausting the air, the pores of 

 he hide being deprived of air, exert a capillary 

 ttraction on the tan, which may be aided by pressure, 

 o that the thickest hides may be tanned in six weeks 

 The operation of bleaching affords another example. 



7. Exerting Forces too large for human Power. 

 Vhen the force of large bodies of men or animals is 

 pplied, it becomes difficult to concentrate it simul- 

 taneously at a given point. The power of steam, 

 lir, or water is employed to overcome resistances 

 vhich would require a great expense to surmount 

 jy animal labour. The twisting of the largest cables, 

 he rolling, hammering, and cutting of large masses 



of iron, the draining of mines, require enormous 



exertions of physical force, continued for considerable 

 jeriods. Other means are used when the force 



required is great, and the space through which it is 

 o act is small. The hydraulic press can, by the 

 ;xertion of one man, produce a pressure of 1500 



atmospheres. 



8. Executing Operations too delicate for human 

 Touch. The same power which twists the stoutest 

 cable, and weaves the coarsest canvass, may be 



imployed, to more advantage than human hands, in 

 spinning the gossamer thread of the cotton, and en- 

 Lwining, with fairy fingers, the meshes of the most 

 delicate fabric. 



9. Registering Operations. Machinery affords a 

 sure means of remedying the inattention of human 

 agents, by instruments, for instance, for counting the 

 strokes of an engine, or the number of coins struck 

 in a press. The tell-tale, a piece of mechanism con- 

 nected with a clock in an apartment to which a 

 watchman lias not access, reveals whether he has 

 neglected, at any hour of his watch, to pull a string 

 in token of his vigilance. 



10. Economy of Materials. The precision with 

 which all operations are executed by machinery, and 

 the exact similarity of the articles made, produce a 

 degree of economy in the consumption of the raw 

 material which is sometimes of great importance. 

 In reducing the trunk of a tree to planks, the axe 

 was formerly used, with the loss of at least half the 

 material. The saw produces thin boards, with a loss 

 of not more than an eighth of the material. 



11. The Identity of the Result. Nothing is more 

 remarkable than the perfect similarity of things 

 manufactured by the same tool. If the top of a box 

 is to be made to fit over the lower part, it may be 

 done by gradually advancing the tool of the sliding 

 rest ; after this adjustment, no additional care is 

 requisite in making a thousand boxes. The same 

 result appears in all the arts of printing : the impres* 

 sions from the same block, or the same copperplate 

 have a similarity which no labour of the hand could 

 produce. 



12. Accuracy of the Work. The accuracy with 

 which machinery executes its work is, perhaps, one 

 of its most important advantages. It would hardly 

 be possible for a very skilful workman, with files and 

 polishing substances, to form a perfect cylinder out 

 of a piece of steel. This process, by the aid of the 

 lathe and the sliding rest, is the every day employment 

 of hundreds of workmen. On these two last advan- 

 tages of machinery depends the system of copying, by 

 which pictures of the original may be multiplied, 

 and thus almost unlimited pains may be bestowed in 

 producing the model, which shall cost 10,000 times 

 the price of each individual specimen of its perfec- 

 tions. Operations of copying take place, by printing, 

 by casting, by moulding, by stamping, by punching, 

 with elongation, with altered dimensions. A remark- 

 able example of the arts of copying lies before the 

 eye of the reader in these pages. 1. They are copies 



