370 SECTION MECHANICS. 



the steam-engine now is, and not only so, but Watt invented the steam- 

 engine indicator, which enables us to ascertain that which is taking 

 place within the cylinder, and to detect whether or not the steam is being 

 economically employed. I have on the table before me a very excel- 

 lent model illustrating an inverted direct acting pumping engine in its 

 complete form, and I have also a model, of French manufacture, the 

 cylinder and other working parts of which are in glass, which shows a 

 form of beam condensing engine at one time common. I do not say, 

 however, that Watt was the first to make the suggestion of attaining 

 rotary motion from the power of steam. Leaving out of consideration 

 Hiero's toy, Papin, as I have remarked, hoped to get rotary movement 

 second hand by working a water-wheel with the water that had been 

 raised by his steam engine ; moreover, as early as 1737, Jonathan 

 Hulls proposed to obtain rotary motion from a Newcomen engine, 

 and to employ that motion in turning a paddle wheel to propel a tug 

 boat which should tow ships out of harbour, in a calm, or even against 

 an adverse wind. I have here one of the prints of his pamphlet, and 

 in order that you may better appreciate Hull's invention I have put 

 an enlarged diagram upon the wall, and I think I may take this as the 

 starting point for saying a few words about the steam-engine as a 

 prime-mover in steam vessels. 



We have in the collection, No. 2150, Symington's engine tried 

 upon the lake at Dalswinton in 1788. Here a pair of single 

 acting vertical cylinders give by the up and down motion of their 

 pistons reciprocating movement to an overhead wheel ; this wheel 

 gives similar motion to an endless chain, which chain is led away 

 so as to pass round two pairs of ratchet wheels loose upon two 

 paddle shafts. By the use of a pair of ratchets the reciprocations 

 of the chain are converted into rotary motion in one direction only, 

 and that the driving direction, of the two paddle-wheels, placed one 

 behind the other. Symington's arrangement for obtaining the rotary 

 motion .always in one direction of his two paddle-wheels is very- 

 similar to that proposed by Jonathan Hulls for his single stern-wheel. 



Want of time forbids me to do more than to just allude to the names 

 of Hornblower and Wolff in connexion with double cylinder engines 

 engines wherein the expansion of steam is commenced in one cylinder 

 and continued in another and a larger one. 



