case, is of little service, yet it is of great use when compounded witli others. Titus, the ‘spokes of a great wheel are all levers, per- petually acting; and a beam fixedto the ax. is to draw the wheel about by men or horses, is a lever. “The lever, also, may be com- binedwith the screw, but not conveniently with pullies, or with the wedge- The wheel and axle is combined with great ‘advan- tageiwith puliies. .The screw, is not well combined with pulliexs; but the perpetual screw, combined with the wheel, is very eer- viceable. Tne wedge cannot be combined with any other mechanical pC',W%r, and it only performs its effect by percussion; but this force of percussion may be increased by en. gmes. ‘ r A» . ’ ~ , Follies may be combined with pnliies, and wheels with wheels; therefore, if any single wheel would be too large, and take up too much room, it may be divided into two’ or three more wheels and trundles, or wheels and pinions, ‘as in Cif>Ci£~WO3‘i{, so as to have the some power, and perform the scone etlbct. In wheels with teeth, the number of teeth that play together in two wheels <>u_v;ht to be prime to each other, that the smietcetli rn 1y not meet at every revolution. For, when different teeth meet, they by degrees Wear themselves into :1 proper figure; Ii'18f€%liJYd they should be co;itrivc;l that the same teeth meet as seldom as possible. - . ' 8. The strength of ‘every part of the nu. chine ought to be in-:1-do propor;io'-.1al,_to the stress it is to bear; and, tlierefbre, let every lever. be im ids so miich stronger, as its length and the weight it is to support is greater. And let its strength diminish pI‘0pOI"£i0.)zLlly from the fulcrum, or point, where the great- est stress is, to each cud. The axles of wheels and pullies must be so much smonger, as they are to bear greater weiglit. “ The teeth of wheels, and the wheels themselves, which act -with greater force, must be pro- portionally stronger; and in any combina- _tion of wheels ‘and axles, make their strength diminish gradually from the weight to thei power, so that the strength of every part‘ be‘ reciprocally as the velocity it has. The strength of ropes must be according to their tension, and that is as the squares of their diameters. And, in general, whatcvertparts a machine is composed of, the strength of every particular part of it must be adjusted totbe stress”upo‘n it. [’I‘here,f‘o,re, in square beams, the cubes of“ the diameters must be made proportional toiithcl stress they bear. And let no part be stronger or bigger thanis necessary for the stress upon it; not on_l_y—for the case and we1l.going of the machine, but for the diminishing the friction. For all rsu. perfluous matter, in anytpart of it, is nothing but a. dead weight upon’ the machine, and serves for nothing but to clog its motion.‘ And he is by no means a perfect mechanic, that does not only adjust the strengthto the stress,;,but.a.lso contrive’ all the parts to last equally well, that the whole machine may fail together. i ‘ * . , 9. A To avoid friction as much as possible, the ma’ch'i-ne ought not-to have any ‘unneces- sary motions,ror useless parts; for :1 multi- plicity of parts, by their weight and motion, increase thefi-icti‘on“. The diéiinetcr of the wheels and pullies ought ‘to be large, and the diameters of the itI_‘bOI‘B‘0I' spindles they run 0 min a weight to any great height, and, in this‘ smooth ; and, when the machine goes, must its friction diminished, by causizfg it to run just to fill their holes. , . the inachine. The resistance of the medium in some rnacln-nos hasa sensible 'ex‘l'c',;t. But. 'portion to the Vimotion of the rnachiuei in on as small as can be consistent withtheir strength. — All ropes and gcords must be as pliahleas. possibl‘e,’an_e:l for that end are rub. -. noun.‘-¢w—.—-o.-.. ,Ja- wt ‘u. .......-.-.. bed with tar or grease ; the teeth of wheels’ must be made to fit and fill up the openings, and cut in the form of epicycloids. All tlio axles, where the motiorr is, and all tooth xvhe-re they work, and all parts that, in work- ing, rub upon one another, must be made he oiled or greased. If a joint is to go pret-_ ty still’ and steady, rubu littleigrease upon it». The axis a (fig, 1)_of a wheel may have on. two‘ rollers, B C, turning round with it, upon two centres. _ Likewise, instead of the teeth of wheels, one muy_pla'ce little wheels,as A B, (fig. 2,_ running upon an axis in itacentre. And this will take away almost all the friction of the teeth. And, in lanterns or trundles, the rounds may be made to turn about, instead of'being‘fi_::ed. i . in all rnncliincs-will: r wheels, the axles. or spindles oughtnot to shnlce, which they wifi do if they be too short ; and their ends ought f When the teeth ofa wheel are much worn away, it makes that wheel move irregularly about, increases the friction, and requires ‘rn:n'<=. force, anti mt-..y cause the teeth oi" two wheels to run foul upon one another, and to stop their motion, rm‘d'endange1'brcnlting the i.i")Ci.i'l'. be tulzen to dress the teeth, andlrecp them to their proper figure. , i . ' l M ' ‘ 10; When. any motionis to be long con- tinned, contrive the power to move or not al. ways one way,‘ if it con be done. For this is better and easier p«2rl'orine£l than when the option is iiterrupted, and the power is forced to move, first one "way and then another, be. cause every new change of friction requires new additional force to effect it. Besides, body in motion cannot suddenly receive a contrary motion, without great violence: and the moving. any part of the ll’1£LCi1l'flG ()OlliI‘c1I‘}' vmys by turns, with sudden jerks, tends only tosbake the machine to pieces.‘ ’ ' — 11. In :1 machine that moves always one vay, endeavor to have the motion unitbrm. 12. But when the nature of the thing rc- quiras that 21 motion is to be suddenly com. municated to a body, or sudcienly stopped, to prevent any clarnage or violence to the en. gine by a sudden jolt, let the three act against some spring, or beam of wood,’which may supply the place of a sprinrr. 13. In regard to the size of the machine, let it be made’ as large as it can convenient- ly. ii ‘The greater the machine, the exncter it will work, and perform all its motions the better. For there will always be some er. rors in the ‘nial«:ing',,afs‘ well as in the route. rials, and, consequently, in. tlieworliing of all these ~mechanical errors bear ‘a less pro. great machines than in little ones, being near.‘ ly .rccipr'ocally as their dianieters,_ supposing they arejmadeivof the same matter,u_,nd with thesztme azcuracy, and are equally wellfi':i- ished‘. Therefbre, in in small machine, they are more sensible, but in a great one almost vanish.-‘ ‘Therefor_e,‘great macliiiies will an.- swcr better than smaller, in all respects cx_-, ccpt in strength; t'or..the‘greatei- the machine the xycalter it is, and lessiiblc -to resist any violence. o — 4 " V V. t V 14. For eiigines that go by Water, it is no. cessary, to . measure ,the1velo_cit;v and force of. L To prevent this, proper care should’ of sticks, 6.50., and observe how far they are carried in at second, or any given time. - ' But it flow through a hole in a reservoir, or sttmtlizig receptacle oi'w.3.te1', the velocity will be ibuntl. from the depth of the hole be-t low the surface. . * Thus, let 3 == 16 :‘._~._fe’t, '2: -~..: velocity of the fluid per second. B :: the arenlof‘ the hole. H 3 height of the -Water; all in feet. Then- the velocity v 2 ,/ 23H ; ~ and its force 2. the weight of the quantity E or HR of Water, or = EB hu_ndred- weight; because a cubic foot is‘: 62;, lbs. avoirdupois. . Also, .2 hogshea:_l_is about 8.} feet, or 5231 lbs. and J. ml is four hogsheads? . , ' b When you have but a -small quantity of .=.=;z<.t.r-:1’, you must contrive it to fill] asyhiglias ycvzi can, to have the greater velocity, and, eonseqiientiy, more Force upon the engine. 15. if vxter is to be conveyecl through iipss to :1 great disrance, and the descent. be ’3.;it small, so much linger‘ pipes must be ise-zl, because the A water will come Sic‘. . ‘and these ouglit not to be made straight. :2‘ in some places ¢lr.uiotl':crs ;» for the quan- ity pt” ‘W€tiGi' conveyed throu.g-l‘; them depends tpon tl:-re bigness of the bore at the str.iigl1t- :5: place. » Pip’:-2s oi’ conduct comic?‘ directly from an ‘:‘1gine, should bemade‘_ot'_:ron, Willi) flanches ietween, or else of';woo:l;‘i'o‘r lead pipes and burst; but pipes next a jettnusl be lead. .’i;3es should not turn oil’ at an angle, but gra- lziully in. a curve; pipes of elm will last :wc:n‘.y,c-r‘ thirty years in the ground; but hey must be laid so deep ’that,the frost may lot lI'£‘.'d.£3i'l.iil€l'l'l, or else tbe.watermus_t be let int, potliervvise the frost» will split them. , i The thickness of any pipe must be as tho’ lio.zn’eter oftheborc, and also as the'dep:h ;'ro‘m the spiiig. Fora lead pipe offi inches bore, and 60 or. 70 feet high, the thickness must be halfan inch’; and in wooden pipes, ‘ll-"a».c=r should not be Cil‘l'v’B‘."l through pipes :"¢«.stc2' iillll} four feet per second, by reasonof the i'ri-etion of the tubes. Nor should it be mucli wire—dr:twn, that is, squeezed through smaller pipes; for that _creatcs a resistance, as the waterway is less in narrow pipes. ' And in pump work, where 3vater« is con-_ veyed lthrough ‘pipes ‘to higher places, the horse; of the pipes_,:‘should not be made too straight upwards, For the straighter they are netaithe ’t-op,j_the less, water will be dis. charged; Vvater into the pump he too straight, for the some reason. ’ he Wider those are, the easier the pump works. When pipes are wind bound, that is, when air is lodged, in themthat tlhcwatercan hard- make ll hole in the top,‘and till" they air "will blow out at the hole, and when the water comes, batter up-the hole ,again.A.jl)_o the some at every eminence, and allthe air mil“ the pipes, the nirwvill be ‘beyond the. em_i.. r,*(,,,ce; but Stgppigzrqr.~th_e.WEitEl‘,"il}e air will ascend to tl1e.highest-part. fIf"<1iI‘ be drivefi 131,- _at*fi»;g,gt," along.>';viit5l1l the water, the nail-bole ptheiwater. To get,théivelo’ci1‘ty,',i