POWER AND EFFECT. 
hour between the piers, trying to get out, but could not till after the tide slackened, having 
been previously drifted astern towards the Inner Harbour several times, thus clearly showing 
the disadvantages the cumbersome paddle boxes and wheels labour under in a strong head 
wind and rough sea; whereas the propeller, from its protected situation in the dead wood 
of the vessel, and being always under water, maintains its power uniformly and steadily, 
—whilst the paddles of the Dart were as frequently out of water as they were in: hence 
an immense loss of power must arise, which undoubtedly accounts for the singular result 
of a trial of the two vessels under precisely the same circumstances of wind and sea, which is 
the only fair way of comparing the merits of the two plans, even supposing them to be 
on the same scale as to size and power.” 
The preceding facts, which are selected (to the exclusion of a mass of similar 
results) because the authorities from which they are derived render them indis 
putable, enable us to close this part of our investigation by the reasonable 
conclusion, that as far as the question can be decided by such trials as we have 
enumerated, there can be no doubt that the performance of the screw has not 
been proved to be inferior to that of the paddle wheel. Until two vessels of the 
same form and power (one fitted with the screw and the other with the paddle 
wheels) shall have made several voyages so as to test their comparative advantages 
in various kinds of weather, this is as far as the most extensive trials of this kind 
could lead us. So desirable an experiment, we are happy to state, the Admiralty 
are in progress of making, having ordered the Rattler steamer, now building at 
Sheerness, to be fitted with engines by Messrs. Maudslay and Field of 200-horse 
power, and with the screw. She will be of precisely the same power and build as 
the Polyphemus, so that this highly interesting question will be thereby set at rest. 
COMPARISON BETWEEN THE POWER AND EFFECT. 
Fig. 23. 
It now becomes our duty to ascertain the relative value of the paddle wheel 
and the screw as regards the proportion 
which the propelling effort bears to the 
power consumed. For this purpose let a b, 
fig. 23, represent a portion of the screw of 
the Archimedes. Now, whether we move 
a b in the direction c d, or at a right angle 
thereto, say in the line f g, the water will 
recede at a right angle to the surface of 
a b. But as the vessel has to move in 
the direction f c g, the same effort only 
will be communicated to the vessel by a 
particle of water at c being impelled to e, as