184.9."! 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



->i; 



viate the jar consequent on straight-edged blades striking the 

 water. 



If I had a new boat to fit propellers to, they should resemble 

 figs. 7, 6, or 17; or I would rather make them like 

 half the foot of a swimming-bird, as fig. 21, in the 

 margin, — the perpendicular sides being next the 

 vessel, that the greatest strain might be nearest to 

 the power. Such blades would not be raised out of 

 the sea by a vessel's rolling, nor, when submerged, 

 be subject to excessive strainings, as common ones 

 are. They would produce no concussion, or but 

 little, on dipping, and would be twice as effective 

 as the same area employed in tlie current form and 

 fashion. 



If the principle were required to be adopted in the present pad- 

 dles, it could be done at a trifling cost. I would remove portions 

 from the upper sides and attach them below, somewhat after the 

 manner shown at figs. 22, 23, 24, and 25. 



Fig. 21. 



Fig. 22. 



Fig. 23. 





Fig. 24. 



Fig. 



The portions 7mght be removed by curved instead of straight 

 lines. 



If I used blades similar to fig. 7, I would Vandyke their lower 

 edges as at fig. 23, point them as at fig. 25, or fork tliem as at 

 fig. 22. 



fTo be continued.J 



DOUBLE-ACTION PUMP FOR WATERWORKS. 



Sir — Having seen a description of an "Improved Pumping En- 

 gine," in Part Itl, page 165, of your Journal, and seeing it there 

 stated that an advantage is gained, "partly by the construction of 

 the pump-valves, and partly by the use of a new kind of pump, 

 lately registered by Mr. Thompson, Messrs. Simpsons' manager," 

 we are led to believe that the public are to take both valves and 

 pump "as new inventions." We think the following remarks will 

 put the matter in the proper light. 



The accompanying engravings show the arrangement used by us 

 for some years past. 



Section of the Valve. 



We were aware that the principle of this pump had been con- 

 •idered to be the invention of Trevithick, but the arrangement of 



a bucket and plunger working in one cylinder we thought to be 

 nevv at the time we used them. In this it appears we were wrong. 



Seer oc of Direct-Action Tump at the Waterworks, Trafalgar.^ luarp. 



fur upon referring to page 281 of "A Description and Histoiii-ttl 



