MACHINERY. 



the unequable motion ot the pitloii, moved in tlie common 

 way bv a crank motion ; but it occalions fuch abrupt 

 changes of motion, that the machine is fhakeu by jolts. In- 

 deed, if the movements were accurately executed, the ma- 

 chine would be foon tbnken to pieces, if the parts did not 

 ^ive way by bending and yielding. Accordingly we have 

 always obferved that this motion foon failed, and was changed 

 for one that was more fmooth : a judicious engineer will 

 avoid all fuch fndden changes of motion, efpecially in any 

 ponderous part of a machine. 



When feveral rtampcrs, piftons, or other reciprocal movers 

 are to be raifed and deprelTed, common fcnfe teaches ns to 

 diftribute their times of adlion in an uniform manner, fo 

 that the machine may always be equally loaded with work. 

 When this is done, and the obfcrvations in the preceding 

 paragraph attended to, the machine may be made to move, 

 almoll as fmoothly as if there were no reciprocations in it. 

 Nothing (hews the ingenuity of the engineer more, than the 

 artful, yet fimple and effectual contrivances, for obviating 

 thofe difficulties that unavoidably ariie from the very nature 

 of tire work to be performed by the machine, or in the 

 power employed to actuate it. 



In the contrivance of machinery, an engineer mull not be 

 tied down by too many inviolable maxims, bccaufe thofe 

 contrivances which are the mod improper in iome fituations 

 will be the beft of all in other cafes. There is great room 

 for ingenuity and good judgment in the management of the 

 moving power, when it is fuch as cannot immediately pro- 

 duce the kind of motion required for efFefting the purpofe. 

 We mentioned tlie converfion of the continued rotation of 

 an axis into the reciprocating motion of a piibw, and the 

 improvement which was thought to have been made on 

 the common and obvious contrivance of a crank, by lub- 

 fiituting a double rack on the piifon rod, and the incon- 

 venience arifing from tlie jolts occafioned by this change. 

 We have been informed of a great forge, where the engi- 

 neer, in order to avoid the fame inconvenience arillng from 

 the abrupt motion given to the gn-at lledge hammer of feven 

 hundred weight refilling with a five-fold momentum, f )rmed 

 the wipers for lifting it into fpirals, which communicated 

 motion to the 'hammer with fcarcely any jolf; whatever : 

 but the refult was, that the hammer rofe no higher than it 

 had been raifed in contaft with the wiper, and then fell 

 on the iron bloom, with very little effeil. The caufe of its 

 inefficiency was not gueffed at ; but it was removed, and 

 wipers of the common form were put i:i place of the fpirals. 

 In this operation the rapid motion of the hammer is abfo- 

 lutely necell'ary ; it is not enough to lift it up, it muft be 

 raifed up fo as to fly higher than the wiper lifts it, and to 

 ilrike with great force the ftrong oaken fpring v/hich is 

 placed in its way. It comprefl'es this fpring, and is re- 

 flected by it with a confiderable velocit) , fo aS to hit the 

 iron as if it had fallen from a great height : had it been 

 allowed to fly to that height it would have fallen upon the 

 iron with fomcwhat more force (becaufe no oaken fcring 

 is perfeftly elaftic) ; but this would have required more 

 than twice the time. 



In employing a power which of necefHty reciprocates, to 

 drive machinery which requires a continuous motion (as in 

 applyintr the Ream engine to a cotton or corn grinding mill), 

 there alfo occur great difficulties. The necedi'y of reci- 

 procation in the firlt mover walles much pfiwer, becaufe 

 the inftrument which communicates fuch an enormous force 

 mull be extremely ftrong, and be well fiippsirted. The im- 

 pelling power is waited in imparting, and afterwards dc- 

 flroying a vail quantity of motion in the working beam. 

 The ikilfu! engineei' will attend to this, and dsi his utmoll 



to procure the neceflary ftrength of this lever, without 

 making it a vail Joad of inert matter. He will alfo remark, 

 that all the Ilrains on it, and on its fupports, are changing 

 their direftions in every ftrokc. This requires particular at- 

 tention to the manner of fupportingit : ifweobferve the old 

 fteam engines which have been long erefted, we fee that 

 they have uniformly fhaken the building to pieces. This 

 has been owing to the ignorance or inattention of the engi- 

 ncei' in this particular ; they are much more judicioufly 

 creftcd now, experience having taught the moft ignorant 

 that no building can withfiand their defultorv and oppofite 

 jolts, and that the great movements mull be fupported by 

 a frame work of wood or iron, independent of the build- 

 ing of mafonry which contains it. The gudgeons of a 

 water wheel ftiould never reft on the wall of the building ; 

 it fliakes it, and if fct to work foon after the building 

 has been ercdled, it prevents the mortar from taking firm 

 bond, perhaps by ftiattering the calcareous cr^-ftals as they 

 form. 



When the engineer is obliged to reft the gudgeons in 

 this way, they fhould be fupported by a block of oak laid a 

 little hollow : this foftens all tremor,'--, like the fprings of 

 a wheel carriage. This practice would be very ferviceable 

 in many other parts of the conltruclion. It will frequently 

 conduce to the good performance of an engme, to make 

 the action of the felilling work, unequable, and accommo- 

 dated to the inequalities of the impelling power. This will 

 produce a more uniform motion in machines, in which the 

 momentum of inertia is inconfiderable. There are fome 

 beautiful fpecimens of this kind of adjuftment in the me- 

 chanifm of animal bodies. 



In many compound machines it is of confequence to be 

 able to detach part of the movements while the others con- 

 tinue in motion. Thus in cotton-fpinning machines, it is ne- 

 celary to be able to call off or ftop any fpind e at pleafure, 

 without dilturbing the reft ; and in a large mill containing 

 many machines, it is effeiitial that any one may be reieafed 

 without interruption to the tirlt mover. Such contrivances 

 are called coupling or clutch-boxes : they are effected in 

 various ways, Iome of which are detailed under Coupling- 

 BOX. But we wifti here to defcribe a recent improvement, 

 very generally adopted in cotton and woollen mil s ; the 

 object of which is to avoid a jerk being given to any m.achine 

 when it is put in a£tion, from its being fuddenly urged from 

 a Hate of reft to a ftate of motion : for if the movement is 

 to be rapid, nothing can be more dellructive to the machine 

 than the violence ot the (hock it receives from the common 

 clutch-box. To avoid this, the arm which gives motion to 

 'he machine when the clutch of the running fpindle is en- 

 gaged wi'h it, is not fixed fall upon the fpindle, but is 

 made in two halves Icre.ved together upon a circular part 

 of the- fpindle, and pinched upon it lo fail by the fcrews, that 

 it will have fufiicieut friction to turn the machii e round in 

 the ordinary courfe of its work, but (lips round upon the 

 (pindle, if the reliltance is greater than this friction, which 

 thus becomes the mealure of the power dealt out to the 

 machine. 



Suppole a machine of this kind at reft, the clutch is turned 

 by the tirlt mover with a confiderable velocity, and is fud- 

 denly connedled wi;h the arm above defcribed : now it re- 

 quires fome time (independent of any refiltance or work of 

 the machine) to put its parts in motion. In this time the 

 arm (lips round upon the Ipindle, but the friction acts con- 

 Itantiy, and with an equable force upon the machine to turn 

 it round. It commences its motion, which gradua'lv acce- 

 lerates, until it arrives at the fame velocity as the driving 

 fpindle, and then the flipping of the box ceafes, and the 

 5 D 2 machine 



