ON THE DEVELOPMENTS OF MECHANICAL ENGINEERING. 497 



used for manufactiTring purposes, but rather to turn at once to those 

 employed for other objects. 



Steam Navigation. — In 1831 there ■were a considerable number of 

 paddle-steamers running on some of the rivers in England and across 

 the Channel to the Continent. But there were no ocean steamers, properly 

 so called, and there were no steamers used for warlike purposes. As in 

 the case of the waggon-boilers, the boilers of the paddle-steamers of 1831 

 vrere most unsuited for resisting pressure. They were mere tanks, and 

 as tanks the downward strain from the mere weight of water was as 

 great on the bottom plates, even in the absence of any steam-pressure 

 within the boiler at all, as, when the steam was up, was the upward 

 strain on the top plates. Under these circumstances, again, from 3^^ lbs. 

 to 5 lbs. on the square inch was all the pressure the boilers were competent 

 to bear, and this feeble pressure, coupled with the slow speed at which 

 the engines ran, caused them to develoji but a small amount of horse-power 

 in relation to their size. Moreover, as in the land engine, the connec- 

 tion between the parts of the marine engine was such as to be incompetent 

 to stand the strain that would come upon it if a higher pressure, with a 

 considerable expansion, were used, and thus the consumption of coal 

 was very heavy ; and we know, that having regard to the then con- 

 sumption, it was said, on high authority, it would be impossible for 

 a steam-boat to cross the j^.tlantic, as it could not carry fuel enough to 

 last out the voyage ; and it was not till 1838 that the Siritis and the 

 Gi-eat Western did make the passage. One boat, it is true, had crossed 

 before, but it was not till 1838 that passenger traffic was really com- 

 menced. In 1831, owing to the condensation being effected by injection, 

 the marine boiler was supplied with salt Water, the hulls were invariably 

 of wood, and the speed was, probably, from eight to nine knots an hour. 

 In 1881 the vessels are as invariably either of iron or of steel, and I 

 believe it will not be very long before the iron disappears, giving place 

 entirely to the last- mentioned metal. With respect to the term ' steel ' I am 

 ready to agree that it is impossible to say where, chemically speaking, iron 

 ends and steel begins. But (leaving out malleable cast-iron) I apply this 

 term steel to any malleable ductile metal of which iron forms the principal 

 element, and which has been in fusion, and I do so in contradistinction to 

 the metal which may be .similar chemically but which has been prepared 

 by the puddling process. Applying the term steel in that sense, 1 believe, 

 as I have said, it will not be very long before plate iron, produced by the 

 puddling process, will cease to be used for the purpose of building vessels. 

 With respect to marine engines these are now supplied with steam from 

 multiple-tubed boilers which are commonly cylindrical. They are of 

 enormous strength and made with every possible care, and carry from 80 

 to 100 lbs. pressure on the square inch. It has been found, on the 

 whole, more convenient to expand the steam in two or more cylinders 

 rather than in one. I quite agree that, as a mere matter of engineering 

 science, there is no reason why the expansion should not take place in a 

 single cylinder, unless it be that you cool down a single cylinder to an 

 extent which cannot be overcome by jacketing, and which, therefore, 

 destroys a portion of the steam on its entrance into the cylinder. As 

 regards the propeller, as we know, except in certain cases, the paddle- 

 wheel has practically disappeared, and we have the screw-propeller 

 emjjloyed, either singly, or in pairs. This substitution of the screw- 

 propeller for the paddle enables the engines to work at a much 



1881. K K 



