STEAM ENGINE. 



387 



the valves of steam engines. In 1801, Mr Bramah 

 contrived the four way cock, as a substitute for 

 the valves, the cock turning always in one direc- 

 tion. 



As before stated, Leupold had projected a high 

 pressure engine, and so had Watt, but it was not 

 until 1802 that the principle was applied with suc- 

 cess, in the simple high pressure engine of Trevi- 

 thick and Vivian, whose principal object seems to 

 have been the formation of a simple and portable 

 engine, where water was scarce, and where economy 

 of fuel was an object of less moment. These en- 

 gines were intended chiefly to propel carriages on 

 railways. In 1804, Arthur Woolf projected a new 

 form of expansion engine, somewhat after the con- 

 struction of Hornblower's, but he used high pressure 

 steam in the small cylinder, whereas Hornblovver 

 did not. Wonderful advantages were expected 

 from Woolf s engine, from the supposed existence 

 of a law in the expansion of steam which he ima- 

 gined he had discovered. He stated that from 

 numerous experiments he had made, he found that 

 the temperature remaining the same the bulk of 

 steam is inversely as the pressure in Ibs. above the 

 atmosphere ; and thus, that steam generated at 

 fifty Ibs. above the pressure of the atmosphere 

 would expand, when allowed to escape into a large 

 vessel of the same temperature, to fifty times its 

 former bulk. But in this discovery he deceived 

 himself, and has led many others astray, for the ex- 

 pansion will be inversely as the pressure ; thus, a 

 cubic foot of steam, generated at a pressure of 50 

 above the atmospheric pressure, will (reckoning the 

 atmospheric pressure at 15 Ibs. per square inch) ex- 

 pand in the proportion of 15 to 15 -f 50, or 15 to 

 65, or 1 to 4^, that is, the steam, when expanded, 

 will only occupy 4^- cubic feet, instead of 50, ac- 

 cording to Woolfs assertion. The engine of Woolf 

 is said, however, notwithstanding this immense de- 

 duction from its proposed advantages, to work bet- 

 ter than the single cvlindered expansion engine of 

 Watt. 



We have thus given a short sketch pf the history 

 of the steam engine, but we have not noticed the 

 many attempts that have hitherto been made to 

 form rotatory steam engines, or steam wheels, as 

 these, however ingenious, have hitherto been fail- 

 ures, and when found to work at all, their effect 

 has been inferior to that of the piston and cylinder 

 engine, employing the same quantity of steam. 

 Much has been said of late in praise of the American 

 steam wheel, the invention of Mr Avery, and which 

 has lately been brought into use by Mr Ruthven of 

 Edinburgh, the inventor of the printing press which 

 goes by his name. The writer of this article has a 

 working model of this engine now before him, which 

 works- very well, and acts upon the same principle 

 as Hiero's steam engine or the Eolopile, the first 

 steam engine ever invented. Mr Ruthven has an 

 engine, which is said to have a power of fifteen 

 horses, now working on his establishment at Edin- 

 burgh, and driving turning laths arid other machinery; 

 but from the many unsuccessful attempts that have 

 been previously made to produce effective rotatory 

 steam engines, from the admirable exposition of 

 the subject by Mr Russel, in the last volume of the 

 Edinburgh Philqsophical Transactions, and from our 

 own experiments, we would not be disposed to be 

 very sanguine as to the speedy and general adoption 

 of the rotatory steam engine. 



Description. In order to make the action of the 

 condensing steam engine easily understood, we will 



draw the attention of the reader in the first place 

 to the most important parts only, and afterwards 

 point out the connexion of these with each other 

 in more minute detail. 



Let there be a hollow cylinder, A, fig. 1, accu- 

 rately bored in the interior, so that it shall be 

 smooth, and of the same diameter from bottom to 

 top. Into this cylinder let a solid piston of metal, 

 B, be fitted so that it may easily move up and 

 down, yet so as not to allow air, water, or steam, to 

 pass. To the centre of this piston let the upright 

 rod, C, be attached, the upper end of which is 

 connected with a long beam, or lever, D E F, 

 poised in the middle E ; to the other end, F, of this 

 beam there is a weight, W, attached. G is a small 

 pipe, also containing a piston similar to that in the 

 large cylinder. The pipe in which this piston 

 moves is closed at the top with a cover or lid, 

 through the centre of which the rod e moves easily up 

 and down, yet so as not to allow any air or steam to 

 escape. A pipe I is led from the boiler and enters 

 the pipe or small cylinder G, near the top, and at 

 the bottom of this cylinder G another pipe enters, 

 leading from the cistern, K, which contains cold 

 water. A connexion is formed between the large 

 and the small cylinders by the cross pipe L. 



LrJ 



Fiy.J 



Let us now suppose that the weight W is so ad- 

 justed as just to draw the end, F, of the beam 

 down, and, consequently, raise the other end D, 

 along with the piston B ; and suppose the small pis- 

 ton to be below the opening L, in which case the 

 steam from the boiler would be allowed to enter 

 the large cylinder, as the piston B ascended. On 

 the piston arriving near the top the beam would 

 strike the tappet e, which would raise the small 

 piston to the position shown in the cut ; when in 

 this positior, it now being above the opening L, 

 the steam from the boiler would be shut off, and :i 

 communication opened with the vessel K, from 

 which cold water would enter the cylinder A, and 

 condense the steam, forminga vacuum below the pis- 

 ton; the atmosphere above the piston then havii/g 

 nothing to counteract its weight, would cause the 

 piston to descend ; on its arriving near the bottom, 

 the beam would strike the tappet f, and cause the 

 small piston to descend below the opening L ; this 

 would stop the communication with K, and admit 

 steam from the boiler, allowing the large piston 

 again to ascend as before. 



This is the nature of the action of the engine of 

 2n2 



