116 LECTURES TO SCIENCE TEACHERS. 



Belidor describes the boiler with the cylinder above it, the 

 beam, the pumps worked at the other end of the beam, the 

 open-topped cylinder with a piston kept tight by water pack- 

 ing, the water injection into the cylinder, and the plug- tree to 

 make the valve self-acting, and to- cause the machine to con- 

 tinue at work. I have also here, lent by Mr. Bennet Woodcrof t, 

 one of the most interesting engravings to an engineer that 

 I know of. It was published in the year 1719, and shows 

 the ' Newcomen engine erected in 1712 at Dudley Castle. I 

 have also before me another model of a Newcomen engine 

 which is of historical interest. This is a model lent by the 

 University of Glasgow, and bears the label that "in 1765 

 James Watt, in working to repair this model belonging to the 

 Natural Philosophy Class in the University of Glasgow, 

 made the discovery of a separate condenser which has 

 identified his name with the steam-engine." 



To Watt we owe, as you know, the condensation in a 

 separate vessel, the parallel motion, steam-jacket, double- 

 action, expansion, the indicator to tell us how the engine 

 is working, and the governor. We have on the table before 

 us, models brought from the collection, and bearing upon these 

 various subjects. 



Passing on from Watt, we get to Hornblower, who in 1781 

 patented the double-cylinder engine, afterwards largely 

 developed by Wolfe. Leaving the general history and going 

 to a particular class of steam-engines, and going back a little 

 in date, I must refer to Jonathan Hulls, who in 1737 pub- 

 lished the pamphlet I have here, in which he shows how, by 

 the use of the Newcomen engine working a stern wheel, a 

 paddle boat could tow ships out of a harbour against an ad- 

 verse wind, or in the absence of any wind. As the engrav- 

 ing appended to Hulls' pamphlet is not large enough to be 

 distinctly visible, I have had a diagram made of it which is 

 upon the wall. Hulls states that he proposed to employ a 

 Newcomen engine, the rectilinear reciprocating motion of 

 which being obtained by the alternate action of the pressure 

 of the air on the piston for one direction, and of the descent 

 of a counterweight equivalent to half the effect of that 

 pressure for the other direction. Hulls employed this to give 

 alternating reciprocating motion to two pulleys placed upon a 

 shaft, from which by means of bands, one being open and 

 the ot'her crossed, motion was to be transmitted to the 



