122 LECTURES TO SCIENCE TEACHERS. 



one crank pin, the cylinders being placed on an A frame ; the 

 construction known for many years as the Thames Tunnel 

 engine. Then we had by Maudslay (and used in the Eichmond 

 steamboat, I think, as long ago as 1827) the oscillating engine, 

 a most compact form, and one which has been largely employed 

 for marine purposes. Here we have a model of that oscillating 

 engine applied " Thames Tunnel " fashion, that is, the two 

 cylinders at an angle of about 45 degrees to the vertical, and 

 their piston rods laying hold of a single crank. We have 

 then in the way of direct engines, the direct overhead engine, 

 where you have a vertical cylinder, and a connecting rod 

 leading up to the crank \ and those engines, or a pair of them, 

 are much used now-a-days as winding engines in collieries, the 

 drum or a pair of drums between the two cylinders making 

 the fly-wheel. Then we have the same kind inverted with a 

 cylinder carried on side frames, and the connecting rod working 

 a crank shaft near the level of the ground, a construction 

 known as the " steam hammer " and largely used in screw 

 steamers. Further illustrative of this construction we have a 

 wooden model of the compound cylinder engine by Messrs. 

 Rennie of the Peninsular and Oriental steamer "Pera," a 

 form of engine which admits of very ready bracing to with- 

 stand the strains which come upon the various parts. 



The locomotive, of course, is a grand example of the direct- 

 acting horizontal engine, and so are most of our agricultural 

 engines. Besides this, we have had the trunk engine which 

 has been very largely used, either in the single trunk or in 

 the double trunk form (a trunk coming out at both ends of the 

 cylinder), where the piston body and the trunks working 

 through stuffing boxes are the guides to take the inclined 

 thrust of the connecting rod. There are doubtless some other 

 instances of direct-acting engines which do not occur to me at 

 the moment. 



Except for the purpose of pumping and for hammering 

 iron, and for matters of that kind, we almost always want 

 the power developed by a steam-engine to be delivered in the 

 form of rotary motion, and one would naturally say, " Why 

 do we make these machines, beginning with reciprocating and 

 ending with rotary iriotion ? why do we not obtain rotary 

 motion to commence with ? " I need not tell gentlemen here 

 that this has been the problem of the mechanician from the 

 time of W att to the present day. I do not propose to enter 



