THE STEAM-ENGINE. 125 



having a fly-wheel and matters of that kind, turn a certain 

 amount of power into heat in your bearings, which had better 

 be employed in driving the machinery, and therefore and also 

 for the purpose of simplicity, if it could be attained, the rotary 

 engine is a thing to be desired. But, commonly speaking, the 

 efforts to obtain a simple engine, end in disappointment, and 

 in much greater complication than prevails in the machines 

 which they are intended to supersede. 



Having made these few remarks on the history of our sub- 

 ject (which remarks have carried me much further than I had 

 intended), I will now ask you to consider with me what are 

 the points to be borne in mind in constructing an economical 

 steam-engine. In the expression " steam-engine," I think I 

 must (although want of time tempts me to do otherwise) 

 include the boiler, that very essential element. Were it not 

 so essential, I would ask you to suppose that by some means 

 we had obtained steam economically, and that the object of 

 the Lecture was to consider how far that steam so obtained 

 could be used with advantage. But I think probably it will 

 be as well that we should devote some little time to the boiler 

 itself. As to the kind of boiler to be used, the first thing to 

 be considered is safety ; the next things in very many in- 

 stances indeed are weight and compactness. When we have, 

 for example, to consider the boiler of a common road locomo- 

 tive like Hancock's, of which I have a diagram on the wall, 

 or when we have to consider the boiler of a locomotive or 

 the boiler of an ocean steamer occupying space which might 

 be filled by cargo paying freight, or when we have to consider 

 boilers put into buildings in the city of London where land 

 lets for a guinea a square foot per annum, we may readily see 

 that the compactness of the boiler is an element which weighs 

 very materially in its construction. There are, however, many 

 cases for other purposes, such as water-works, large cotton- 

 mills, and establishments of that kind where the engine con- 

 structor is at liberty to give the boiler any size and weight 

 he thinks necessary, so that occasionally we have to take 

 into consideration the question of compactness, and occasion- 

 ally it is a matter of comparative indifference. In old days 

 (which, I am sorry to say, means when I was an apprentice) 

 the kind of boiler commonly in use for land engines was 

 the waggon boiler, a boiler set over the fire, the products of 

 which went under the boiler bottom to the end, and origi- 



