FRICTION OF THE SCREW. 
35 
a position where such a current exists, has a force acting against its surface, so 
that, although it really slips through the fluid against which it exerts its power, 
its motion in relation to the surrounding and inactive water seems to coincide with 
the action of a screw in a solid body, and, as in the instance alluded to, even 
to exceed the progress which such a screw would make. 
FRICTION OF THE SCREW. 
If we decrease the pitch of the screw, the angular loss will be proportionably 
decreased, so that it may, as we have stated, be reduced below that of the paddle 
wheel; but as we decrease the pitch we encounter an increase of surface friction, 
the amount of which it becomes important to determine. Colonel Beaufoy’s expe 
riments furnish data for determining this kind of resistance; but as the form of 
a screw would lead to a complicated calculation, Mr. Brunei, jun., made some 
experiments with a disc c, fig. 28, equal in diameter to the screw of the Archimedes, 
Fig. 28. 
namely, 5 feet 9 inches, having nearly one-half cut away, which he caused to 
revolve at different velocities, and found the amount of power consumed in turning 
it to be in the proportions given in the following Table: