MECHANICS. 



Without the expenditure of any me- 

 chanical force. 



This was the principle from which 

 the earlier steam- engines derived their 

 efficacy. In the engine constructed by 

 Savery, about the year 1700, the at- 

 mospheric pressure was used for eleva- 

 ting water into a tube, in which a va- 

 cuum was produced by first blowing 

 the air out by means of hot steam ; and 

 when the tube was filled with pure steam, 

 and the air had been completely expelled 

 through a valve which opened outwards, 

 the steam was condensed by cooling the 

 external surface of the vessel which 

 contained it. A vacuum was thus pro- 

 duced, into which the air was prevented 

 from entering, by the circumstance of 

 the valve opening outwards ; and, con- 

 sequently, the pressure of the atmos- 

 phere on the surface of the water in 

 the well or reservoir, forced it up into 

 the vessel or tube. 



Shortly after this, Newcomen used 

 the same means of producing a vacuum 

 in his atmospheric steam-engine, but 

 availed himself of the atmospheric 

 pressure in another way. He provided 

 a cylinder and a piston moving steam- 

 tight in it. He connected the piston 

 rod with the end of a great beam turn- 

 ing on a centre, the other end of which 

 was connected with pump-rods, which 

 he proposed to work. The weight of 

 the pump -rods was sufficient to draw 

 the piston to the top of the cylinder. 

 He then filled the cylinder with steam, 

 by which the air was blown out. 

 Upon cooling the cylinder, the steam 

 was condensed, and a vacuum was 

 produced beneath the piston ; and, con- 

 sequently, the atmospheric pressure 

 taking effect above it, forced it down 

 and drew up the pump-rod at the op- 

 posite end of the beam, and so the pro- 

 cess was continued. 



In this case, the direct or elastic force 

 of steam was not employed, the atmos- 

 pheric pressure being the effective 

 agent, but receiving its efficiency 

 from the vacuum produced by the 

 condensation of the steam. At a 

 much earlier period, however, the 

 mechanical agency of steam, arising 

 from its elasticity, was suggested as a 

 power, whose extent was almost un- 

 limited. In 1663, the then MARQUESS 

 OF WORCESTER asserts that he con- 

 structed a machine which raised a great 

 quantity of water to a considerable 

 height, and which was more powerful 

 than the atmospheric pressure, inas- 

 much as this could only act through a 



limited space : whereas the elastic force 

 of steam " hath no other bounder than 

 the strength of the vessels which con- 

 tain it." 



In modern times, the improved steam- 

 engines, commonly called low pressure 

 engines, employ both the powers of 

 steam which we have mentioned. A 

 piston is moved in a cylinder, and the 

 elastic force of steam acts on one side 

 of it, while a vacuum is produced by 

 the condensation of steam on the other 

 side, and thus the piston is urged 

 forward. 



In high pressure engines, the elastic 

 force of steam is used to urge a piston 

 against the atmospheric pressure on 

 the opposite side. The advantage which 

 this has over the low pressure engine 

 is, that all the apparatus for condensing 

 the steam, in order to produce a vacu- 

 um, is dispensed with, and the machine 

 is consequently cheaper and lighter. 

 On the other hand, it is attended with 

 the disadvantage, that all the elastic 

 force of the steam which is expended 

 in balancing the atmospheric pressure 

 is lost, since that pressure must be 

 overcome before motion is produced ; 

 and, consequently, it becomes necessary 

 to use steam of a very high temperature 

 and pressure in these engines, which 

 increases the expense of fuel, and ren- 

 ders the operation more dangerous. 



Having once obtained, in any of the 

 ways which we have mentioned, the 

 power of moving a piston in a cylinder, 

 it will be no difficult matter to apply 

 that power by a working-beam, or va- 

 rious other ways, to any mechanical 

 purpose. 



In this First Treatise, we have merely 

 attempted to give the reader a suc- 

 cinct account of the most important 

 properties of motion and force, and 

 to offer a rapid sketch of the principal 

 mechanical agents, or first movers. 

 Our design being that the treatise 

 should be adapted for the more popu- 

 lar purposes, we have not entered into 

 any mathematical details on the subject ; 

 and in the same popular form, we pro- 

 pose, in the Second Treatise, to give 

 an account of the Elements of Ma- 

 chinery, or the means whereby the na- 

 tural powers which we have explained 

 here, may be rendered available for 

 mechanical purposes. In that treatise, 

 the MECHANIC POWERS will hold a 

 prominent part. 



