401 



MACHINERY, COMPOSITION OF. 



MACHINES, CALCULATING. 



402 



revolve in, or upon, a straight piece of gearing, for the purpose of 

 changing a continuous rotary to a horizontal motion, or vice rersd ; or, 

 again, the wheels may be susceptible of motion in alternate directions, 

 or they may be intended only to revolve in one, in which case they 

 either are made of such a form as themselves to act as ratchet wheels, 

 or they are prevented from turning in the wrong direction by such a 

 contrivance. In some cases also motion is given by the mere friction 

 of the peripheries of the wheels upon one another, but evidently this 

 can only be accomplished in very small machinery, or where the force 

 to be transmitted is small. The principles upon which wheels of 

 the various descriptions above-mentioned must be formed have been 

 elaborately discussed in Camus, ' On the Teeth of Wheels,' by J. T. 

 Hawkins, 1842 ; Moseley's ' Mechanical Principles of Engineering,' 

 1843; Warr's 'Dynamics,' &c., 1851; they will also be found in a 

 condensed form under GEARING ; MACHINE ; WHEELS, TEETH OF. 



Spindles, or shafts, are the axes upon which the various wheels are 

 fixed, and by which the initial motion is distributed as may be desired. 

 They may be of wood, or of metal ; and if of the_latter class of materials, 

 either solid or hollow, square, hexagonal, or circular, as may be desired ; 

 the object to be aimed at being, in all cases, to make the shaft as light 

 as possible consistently with the requisite degree of strength, and to 

 reduce the dimension of the bearings to the minimum in order to 

 diminish the friction. When shafts are made to revolve on a vertical 

 axis, they turn on a pivot, or gudgeon ; when horizontal shafts of great 

 length are used, they turn in plummer blocks, or carriages. As it has 

 been found practically that two loaded surfaces work upon one another 

 with the greatest amount of friction when they are of the same 

 t material, it is usual to make the bushes or steps, in which the shafts or 

 gudgeons work, of a different material to those parts of the machinery 

 themselves ; or in fact to make iron work on brass or gun metal, wood 

 upon iron, &c. 



Cranks and excentrics are the contrivances by means of which, in 

 addition to wheels, the direction, or the nature, of the initial motion 

 of a machine is transmitted to the work ; or in other words, by means 

 of which circular, and rectilineal, motion are reciprocally converted, or 

 uniform velocity is changed into a variable one. The bell crapk lever 

 is the best illustration of the parts of machinery for transmitting a 

 rectilineal motion in one direction to a shaft working in another direc- 

 tion ; and according as the other end of that shaft may be attached to 

 a crank working on a fixed axle around which it may revolve freely, or 

 be attached to a part of the machine susceptible only of rectilineal 

 motion, it will be able to convert the original rectilineal motion into 

 another one of the same description, or into a curvilinear motion. The 

 rack and pinion have been already cited as an illustration of the means 

 of converting circular into rectilineal motion ; and the common bow 

 drill may be cited as an ordinarily adopted method of converting 

 alternate rectilineal motion into alternate circular motion. Excentric 

 wheels are, however, the most generally adopted means of converting 

 curvilinear into rectilinear motion, and they may be either formed of 

 circular wheels keyed upon shafts, whose axes do not pass through the 

 centre of the former ; or they may be what are called heart-shaped 

 eccentrics ; or they may communicate movement by pins working in 

 slots. The cam is a contrivance frequently used for the purpose of 

 converting continuous circular motion into an alternate vertical one, 

 and this is effected in the case of tilt hammers by means of a series 

 of eccentrics able to lift a lever, fixed at one end, in a gradual manner 

 through a path corresponding to the highest point of the cam itself, 

 after attaining which the lever is suddenly released, and of course falls. 

 Varying rectilinear motion may be produced by modification in the 

 shape of the cam in any way which may be required ; and there are 

 countless modifications of the traverses of machinery, whereby con- 

 tinued alternate motion is obtained from wheels or axles revolving in 

 a circle. A reversing motion may be obtained by the use of a sliding 

 bush working in a groove ; and in the numerous tool-making machines 

 of Mr. Whitworth, every description of change of motion from circular 

 to horizontal may be observed. The crank is, it may be added, the 

 most important element of machinery for the purpose of converting 

 an alternate vertical, or horizontal, motion round a fixed centre, into 

 a circular motion ; and the parallel rods, so universally applied to 

 connect the piston heads to the balance beams of steam engines, may 

 be cited as amongst the most important combinations for the con- 

 version of alternate vertical motion into a partial alternate circular 

 motion round a fixed axis. CRANK; PARALLEL MOTION; STEAM 

 ENGINE. 



Drums and band-wheels are contrivances by means of which motion 

 is communicated from one shaft, revolving on its axis, to another able 

 also to revolve in a parallel direction, and either in the same" or in 

 opposite directions, through the interposition of straps of leather, 

 gutta-percha, or elastic web. The advantage of this method of trans- 

 mitting power is, that directly the resistance to be overcome exceeds 

 the adhesion of the strap upon the band-wheel, the former slips, and is 

 unable to produce motion ; whereas when teethed wheels are used, if 

 the resistance should be suddenly increased, there is a danger of pro- 

 ducing a rupture, or at least a serious derangement, of the machinery. 

 On the contrary, there U often a practical inconvenience in the use of 

 traps, from the extension of the materials of which they are composed ; 

 nd it ia not therefore customary to resort to their use in heavy or 

 mportant machinery. When it ia desired to change the direction of 



ABTS ASD SCI. DIV. VOL. V. 



motion of the shafts, the bands are crossed ; and it is essential that, 

 wherever it is possible so to do, the faces of the wheels should present 

 slightly convex surfaces, in order to keep the bands steady. Band 

 wheels, equally with teethed wheels, admit of an infinite variety of 

 velocity combinations, of which the speed pulleys of the turning lathe 

 may be cited as characteristic illustrations. Among practical men, 

 the first motion band wheel is usually called the diiim, and the second 

 wheel is called the pulley; and the pulleys, where more than one are 

 used, may either be fixed or loose, and made to work, by means of 

 ratchets or of clutches, in any way that may be required. 



Clutches, or the other varieties of loose coupling gearing, are used 

 for the purpose of connecting or disconnecting parts of a machine when 

 it may be desired to start its motion at will, or to arrest the same ; 

 whilst boxed couplings, or fixed connections, are used when the 

 respective parts are intended to revolve continuously. The fast and 

 loose pulley, the friction clutch, and the conical friction and reversing 

 gear, have been introduced in order to obviate the danger which 

 attends the abrupt connection of moving gear with portions of a 

 machine in repose ; but in spite of the inconvenience arising from 

 this cause, and of the danger of stripping the teeth of cog-wheels when 

 suddenly connected, through the inertia of the materials themselves, it 

 is almost constantly the practice to allow the follower to fall upon and 

 to fit into, the driver by means of a series of projections and recesses. 

 Clutches or couplings should be placed as near to bearings or plummer 

 blocks as possible, in order to secure the greatest possible amount of 

 rigidity in the portions of the shafts connected. 



After all, the most satisfactory way of explaining the construction of 

 machinery is to refer to the best examples of the means of superseding 

 the necessity for mere brute or manual labour ; and a description, such 

 as may be found in Warr's 'Dynamics,' of the recently invented 

 turning-lathes, planing, punching, boring, drilling, screwing, and wheel- 

 cutting machines, of the Nasmyth's hammer [HAMMER, POWER AND 

 STEAM], and of the ' Times ' printing machinery, will therefore teach 

 the general reader far more of the power, the advantages, and the 

 details of those various important inventions than any abstract remarks 

 on the principles connected with them could do. The technical reader 

 would also find it advisable to refer to special treatises on these subjects 

 rather than to confine himself to general remarks ; and he is therefore 

 referred, in addition to the works already mentioned, to ' Buchanan on 

 Mill-work,' new edition by G. Rennie ; Coriolis, ' Mdcanique des solides,' 

 &c. ; Hachette, ' Trait^ des Machines ;' Borgnis, ' Traite" des Machines ;' 

 and the various works which treat of the. application of the power of 

 the ordinary prime movers, such as steam, water, wind, horse, or man's 

 power. [MoviNU POWER.] Much information on these subjects is 

 also to be obtained from the ' Mechanic's Magazine, the ' Transactions 

 of the Society of Arts,' the ' Engineer,' and from Armangaud's ' Publi- 

 cation Industrielle des Machines,' &c., Sic. 



MACHINES, CALCULATING. Before computers had attained 

 great proficiency in performing arithmetical operations by the pen, 

 machines by which the results of such operations could be obtained by 

 inspection were in almost constant use. The Roman abacus [ABACUS] 

 continued to be employed in the south of Europe till the end of the 

 15th century, and in England to a later period. An account of the 

 prismatic rods invented by Napier for the performance of arithmetical 

 operations is given under NAPIER'S BONKS ; and the nature and use of 

 the logarithmic scales, under SLIDING RULE. 



The celebrated Pascal constructed, it is said, when only nineteen 

 years of age, a machine for executing the ordinary operations of 

 arithmetic. It was an assemblage of wheels and cylinders. On the 

 convex surfaces of the latter were the numbers with which the opera- 

 tions were to be performed : these operations consisted chiefly in the 

 addition and subtraction of sums of money having the denominations 

 of livres, sous, and deniers, for which may be substituted pounds, 

 shillings, and pence ; and to those denominations the numbers were 

 adapted. Extending round the convex surface of the first cylinder on 

 the right hand of the machine, and one above the other, were the two 

 series, 



0, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 

 11, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10; 



the first of which served for the subtraction and the other for the 

 addition of pence ; the cylinder being turned in the same direction for 

 both operations. Upon the surface of the next cylinder on the left 

 were the two series, 



0, 19, 18, 17, 16 1 



1, 0, 1, 2, 3 18; 



serving for the like operations on shillings : and on the left of this 

 last were several cylinders, about each of which were the two series 



0, 9, 8, 7, 6, 5, 4, 3, 2, 1 

 9, 0, 1, 2, 3, 4, 5, 6, 7, 8; 



and these were used for operations with pounds, or with any numbers 

 in the decimal scale. Attached to the axles of the first cylinder was a 

 wheel having on its circumference 12 teeth ; on that of the second, 

 one having '20 teeth ; and on the axle of each of the other cylinders 

 was a wheel having 10 teeth. Before an operation commenced, the 



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