THE STEAM-ENGINE. 171 



we ought therefore by an expenditure of '17 Ibs. of that coal 

 to obtain one horse-power for an hour, while the very lowest 

 consumption that I know of is 1J lb., therefore the ratio be- 

 tween those two figures is 9 to 1, so that at the present time 

 the best engines use but one-ninth of all the heat which is 

 theoretically given forth by the coal. We see, therefore, 

 there is before mechanical engineers a very large field for 

 improvement. Do not imagine that I am suggesting that we 

 shall ever obtain the whole of the theoretical effect or any- 

 thing bordering upon it. Certainly not by the steam-engine, 

 for we do not yet know of materials which would admit of our 

 commencing with a pressure where the steam would be of a 

 density equal to that of water, nor could we tolerate cylin- 

 ders of such size as to enable the expansion to be carried on 

 until the temperature of ice was attained ; and yet those two 

 conditions, I believe, are necessary before we can even theo- 

 retically get as a useful effect the whole heat of the fuel, but 

 the efforts of mechanical engineers and of men of science for 

 the improvement of the steam-engine have not been barren of 

 results in the past, and will not, I trust and believe, be fruit- 

 less in the future. We are led to be hopeful when we recol 

 lect that within the last fifteen years the consumption in 

 ocean steamers has been brought down from 5 Ibs. of coal per 

 gross indicated horse-power, to 2J, 2, and even 1J Ibs. in 

 real regular ocean steaming; and we have in the case of her 

 Majesty's ship Briton when steaming at half-power, seen the 

 consumption as low as 1 J Ibs. of coal per gross indicated horse- 

 power per hour, which is, as I have said, the lowest that has 

 come under my notice in a real working engine. Is it too 

 much to hope that greater economy will yet be reached ? 



I must now bring these two lectures to a close, and in 

 order that they may lead to some practical result I will at 

 this, their very conclusion, ask you, bearing in mind the 

 progress which has already been made, to look at the pair of 

 indicator diagrams to which I now point. These show the 

 immense difference in consumption of steam (and therefore of 

 coal) between two engines, the one (of no progress) working 

 non-expansively and non-condensing, and the other (the 

 engine of progress) working expansively and condensing. 

 Too frequently, from a desire both in the engine-maker and 

 in the engine-user to save a few pounds in the first cost, 

 wretched machines such as the non-expansive non-con- 



