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MR. D. NAPIER’S PROPELLER. 
Swiftsure at the rate of nearly a mile per hour; and as the former has never 
exceeded 7 miles, we may conclude that the speed of the Swiftsure did not on 
that occasion much exceed 6 miles per hour. 
mr. David napier’s propeller. 
Fig. 53. 
Fig. 54. 
LI t 
Though the object of this article is more particularly to investigate submarine 
propellers, yet the experiment made by Mr. Napier is so closely allied to them 
in form and effect, that we feel it our duty to describe it. 
Figs. 53 and 54 represent this method of propelling, which requires little 
explanation. The difference consists principally in their being only partially 
immersed, the object of which is to reduce the velocity of the propeller axes, 
and to avoid the angular loss produced by the rotation of the parts near the centre.