MACHINERY. 



between the drum and it? piillies, but the other is not, 

 therefore one pair cf the live or dead pullies are always re- 

 volving in one direftion, and the others are turning in an op- 

 poiite way. Both ftraps are cond'ifted through guides fixed 

 to afiidiiig rail, by which the ftraps can be (hiited both at 

 once, lldewavs. When this rail is in a pofition that the ftraps 

 are both upon their dead pullies, the axis and brake wheel 

 are at rell, and in this pofition the rail has a tendency to re- 

 main, unlefs forced by hand. On moving the rail one way 

 from the quiefcent point, one of the ftraps is thrown on its 

 live piillev, and the fpindle tuims with it, winding up the 

 baflcet. By moving the rail in the other direction beyond its 

 quiefcent point, this ftrap is Ihifted on to its dead pulley, 

 and becomes inactive ; but the other ftrap operates on its live 

 pulley, to turn the fpindle in the oppollte direftion, and lets 

 down the ballvet. We ftiall defcribe this very ufefuland curious 

 machine in its place among the cotton machinery. See Ma- 

 nufacture of Cotton. 



Logwood rafping engines, fcrew prefTes, and fome other 

 machines, require a motion to work, them forwards to a cer- 

 tain extent, and then the direftion is to be reverftd to draw 

 them back, which requires but very little power to efteft it. 

 In this cafe the motion may be effefted by a pair of cog- 

 wheels turning each other, and thus communicating the mo- 

 tion for one direilion in which it is to perform the work. A 

 couple of pullies are fixed on the refpettive axes near the cog- 

 wheels, and an endlefs ftrap connefts them, but the ftrsp is 

 fo long, that when the cog-wheels are in gear, the ftrap hangs 

 flack, and does not operate : but to reverie the movement, the 

 fockets for one of the gudgeons of the driving fpindle or 

 axis is made to fhift, that the diftance between tlic centre of 

 the two wheels may be increafed, fo as to difengage the teeth 

 of the wheels, and the ftrap becomes tight, and turns the 

 wheels back ; but on bringing the wheels together again, 

 the ftrap becomes flack, and the wheels refume their original 

 courfe. 



Screws are, of all the mechanical powers, the moft fre- 

 quently ufed iw machines, though not always as moving 

 pans, being chiefly introduced for uniting and retaining the 

 parts. They are not fo conftantly employed as acting move- 

 ments, on account of their friflion, and the trouble of making 

 them ; they are, neverthelefs, a very ufeful agent on many oc- 

 cafions, and poflefs the advantage of accurately retaining 

 any movement they make, and producing an extremely flow 

 motion with eafe, and, when it is required, with the moft per- 

 fect accuracy. No engineer will employ fcrews for a rapid 

 motion, as their friftion and great wear renders them unfit 

 for fuch filuations. To the endlefs fcrew afting on the teeth 

 of cog-wheels, this objection does not apply fo forcibly, be- 

 caufe the great number of teeth on which the fcrew operates 

 fucceflively, do not wear fo faft as the nut of a female fcrew 

 would under the fame circuinftances, and the frittion is far 

 lefs, becaufe the fcrew is not enclofed all round its thread. 

 The endlefs fcrew or worm is ufeful on many occafions to ob- 

 tain a flow motion, which it does in a very fimple manner ; 

 but, for the purpofe of obtaining a quick motion, it ftiould 

 never be ufed, on account of the friftion and confequent 

 wear. This is leen in the common roaliing jack. 



In many fituations in which movn'g fcrews are ufed, the 

 fameeffetts maybe produced in the moft fimple and convenient 

 manner by Mr. Braniah's method of producing and applying 

 a more confiderable degrte of power to all kinds of machinery 

 requiring motion and force, than by any means at prefent 

 practifed for the purpofe This method, for which, on the 

 3 I ft of March 1796, he obtained a patent, conlills in tlie 

 application of water, or other denfe fluids, to various engines, 

 fo as, in lome inftanccs, to caufe them to ECt with immenfe 



force ; in others, to communicate the motion and powers of 

 one part of a machine to fome other part of the fame ma< 

 chine ; and laftly, to communicate the motion and force of oce 

 machine to another, though removed to a great diftance from 

 each other, and where their local fituations preclude the ap- 

 plication of all other methods of connection. The principle 

 of this invention is the fame with the hydroftalic paradox, but 

 its various applications to uleful purpoles is due to Mr. 

 Bramali. The liinplell form is for a pix-fo, or machine, to raifc 

 an enormous weight to a fmall height : a metallic c)linder 

 fufficiently ftrong, and bored perfectly imooth and cylin- 

 drical, IsiS a fi'lid pifton f.tted into it, v iiich is made per- 

 fectly watertight, by leather packing round its edge, or other 

 means ufed in hydraulic engines. The bottom of the cylinder 

 mull be made fufficiently ftrong, with the otiier parts of the 

 iurface, to refift the greateft (train which can ev>;r be applied 

 to it. In the bottom of the cylinder is ii.ferted the cud of a 

 fmall tube, the aperture of which communicates with vUit 

 infide of the cylinder, and introduces water or other fluids 

 into it : the other end of the pipe communicates with a fmall 

 forcing pump, by which the water can be injefted into the 

 cylinder under its pifton : the pump has of courfe valves to 

 prevent the return of the water. Now fuppofe the diameter 

 of the cylinder to be twelve inches, and the diameter of the 

 pifton of the fmall pump or injeiftor only one quarter of an 

 inch, the proportion between the two furfaces or ends of the 

 faid piftons will be as 1 to 2504 ; and fuppofing the inter- 

 mediate fpace between them to he filled with water, or other 

 denfe and incompreffible Huids, any force applied to the fmall 

 pifton will operate upon the otiicr in the above proportion, 

 ^•/^;. as I to 2304. Suppofe the fmall pifton or injector to 

 be forced down when in the a£t of forcing or injecting with 

 a weight of 20 cwt. wliich can eafily be done by means of a 

 long lever, the piftcn of ihe great cylinder would then be 

 moved up, with a force equal to zocwt. multiplied by 2^04. 

 Thus is conftruiited a hydro-mechanical engine, whereby a 

 Vv'eight amounting to 2304 tons can be railed by a fimple 

 lever, in much lefs time through equal fpace, than could be 

 done by any apparatus conftructed on the known principles 

 of mechanics, and it may be proper to obfcrve, that the effect 

 of all other mechanical combinations is counteracted by an 

 accumulated complication of parts, which renders tliein in- 

 capable of being uletully extended beyond a certain degree, 

 .but in machines adted uj.oii, or conftrudted on this principle, 

 every difficulty of this kind is obviated, and their power 

 fubjett to no finite reftraint. To prove this, it will be only ne- 

 ceflary to remark, that the force of any machine ading upon 

 this principle can be iwcieafed, ad infinitum, either by ex- 

 tending the proportion between the diameter of the injeilor 

 and the great cylinder, or by applying greater power to the 

 lever actuating the fmall pump. On this principle very won- 

 derful eiFefts may be produced inttantaneoufly, by means of 

 comprefted air. Suppofe a large cyhnder, furnilhed with a 

 pifton in the fame manner as before defcribed, a globular 

 vefFel is ufed, made of copper, iron, or other ftrong material, 

 capable of refifting immenfe force, fimilar to thofe ufed for 

 air guns : it has a ftrong tube of fmall bore, in which is a 

 ftop-cock : one of the ends of this tube communicates with 

 the great cylinder beneath its pifton, and the other end with 

 the globe. Now fuppofe the great cylinder to be of the fame 

 diameter as that before defcribed, and the fmaU tube equal 

 to one quarter of an inch diameter, wlijch is the fame as the 

 injedting pump before-mentioned fur the prefs : then fup- 

 pofe that air is injedted into the globe (bv the cornmoD me- 

 thods) till it prclles agalnll the co^k with a force equal 

 to 20 cwt. which can be done ; the confequcnce will be, 

 that when the cock is opened, the pifton will be inftantiy 

 b iriGvtd 



