CHAP, ix.] VARIOUS APPLICATIONS OF STEAM. 487 



the tubes. The power of these engines is small, they are made of 

 one or two up to eight horse-power. There is not therefore any 

 necessity for so large a heating surface as in the locomotive, so the 

 tubes are larger and fewer in number. 



The engine works at high pressure and without condensation, the 

 steam being allowed to escape in the chimney so as to produce a draught. 

 The draught ought never to be so great as to draw from the grate 

 any lighted cinders, especially as these engines are employed in the 

 neighbourhood of inflammable substances when engaged in agricul- 

 ture, otherwise there would be a danger of fire. 



Portable engines are not at all economical ; they consume eleven 

 to thirteen pounds of coal per hour for each horse-power. We have 

 already said they are light, in fact the weight of an engine of four or 

 five horse-power is not more than two tons. 



VII. VARIOUS APPLICATIONS OF STEAM. 



We have just 'seen what the steam-engine is ; on what physical 

 and mechanical principles its construction rests ; and what are the 

 various forms it has taken so as to be accommodated to the different 

 services required of it in manufacturing industries, in t/ransport by 

 land and sea, in public works and in agriculture : it remains for us to 

 say a word on the applications themselves to which steam is put 

 and the immense part it plays in modern society. 



The earliest steam-engines were employed as we have seen, to 

 drain water from mines ; they were the motors of powerful pumps, 

 and they still serve for the same purpose. In large towns steam- 

 engines are used to pump the water required for public and private 

 use from the rivers and streams. 



In England and Holland, steam-engines are employed to work the 

 ^pumps that drain marshes and lakes, such as the lake of Haarlem, 

 Zuid Plas ; and the draining of the whole of the Zuyder Zee in the 

 same manner is now spoken of. 



The portable engine is everywhere employed now in public works ; 

 it raises the monkeys of the pile-drivers for building foundations on 

 piles ; the hoists in buildings, railway and seaport cranes. Steam m 

 moves the tow-boats or tugs of rivers and canals, ferry-boats and fire- 



