00 NAVAL SCIENCES. 



1823. He suggested the application of the Archimedean screw to the 

 marine steam-engines, but obtained no success ; until at last the idea was 

 carried into effect in England by Ericson and Smith, The earliest screws 

 were constructed on the plan shown in pi. 19, fig. 28. They were simple 

 Archimedean screws, only one thread winding around the axis; afterwards 

 two threads were made use of {fig. 29), forming a double screw. The 

 steam propeller Archimedes, in England, had a screw of the first kind. At 

 a later period the plan was adopted of removing the inner parts of the 

 screw which greatly increased the lee-way, and employing only segments 

 of the screw. Meantime Ericson had applied three strong arms to the axis 

 of the screw, in the direction of the threads ; six curved segments were then 

 bolted on the outer edge of the screw, which taken together formed nearly 

 a whole circumference of the axis. The mean angle of inclination is 45°. 

 The method adopted in the galliot Napoleon (which is shown as seen from 

 above \^ fig- ^', fig- 3, in longitudinal section; whilst ^g". 4 represents the 

 stern parts, with the screw) is a combination of Ericson's system and of the 

 screw {fig. 28), the segments, of which there are three, contracting to a con- 

 siderable degree on the inside, and joining the axis by a wave line, which is 

 well adapted to cut the water to advantage, without causing too much lee- 

 way. Fig. 5 shows the construction of the wooden model for the four-bladed 

 screw, first employed in the galliot Napoleon. Two double-armed fans, C, 

 of wood were attached to the axle. A, and spreading out from bb^b^, and 

 a a} a^ The segments or blades of the screw are thus formed, and are 

 afterwards completed by the addition of the surfaces B, B\ B'"^, B^ curved 

 from the side; these segments are seen at a}b^&d^, abed, a'^b'^c'^d^, and 

 a b^c^ d^. The three-bladed screw {fig. 6) was subsequently adopted, of 

 which a front view is shown in fig. 7. Here the blades B, B', B*, are 

 placed on the axis. A, with the surrounding lines, abed, a^b^c^d\ and 

 a"^ ¥ c^ d^. The form which nature gives to aquatic animals was closely 

 studied by George Rennie, who noticed that it expands towards the hinder 

 end, like the tail of a fish for instance, while the other parts almost all run 

 together in a point. Following this law, he gave his screw a conical form, 

 making the surface an inclined plane which winds around a cone, so that 

 the threads should be tangents to its surface. PL 19, fig. 8, is a side view 

 of a conical screw, with the continuous blades, ee ; fig. 9 is a front view; 

 fig. 10 is a side view of such a conical screw, with separate blades, ee ; and 

 fig. 11 a front view of the same. Fig. 30 is a view from above of Smith's 

 propeller, which is intended as a substitute for the Archimedean screw, and 

 fig. 31 is a side view of the same. Around the axis, n, is a disk, to which 

 the bearers, mm, are attached, each couple of which supports a platform, 

 like the steps in a treadmill. 



In the section of the galliot Napoleon {fig. 2), A is the bowsprit, B the 

 head, C the cabin for the crew, D the boatswain's cabin, E the foremast, 

 F the stairs to the cabin for the forward deck passengers, G the cabin, 

 H the prison, I the steam chimney, J the boiler, K the main-mast, L the 

 steam engine, M stairs to the engine, N fly-wheel and pinions for the axis 

 of the screw, O engineer's cabin, P officers' and passengers' cabin, R cabin 

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