FROM THE ENGINE TO THE SCREW. 
49 
Fig. 36. 
i and j. They are conical at the parts f and e, and cylindrical at the parts g and h. 
The diameters are one-fourth of the large cones b b. The axis i is the screw axis, 
and j the adjusting axis; k is a spring, which, by means of screws, can be made 
to force the cone f towards the axis c c. If, therefore, we suppose a given force to 
be thus communicated, it will advance the surfaces of the cones together with four 
times the pressure there is exerted at k. In this condition of the parts, if the 
engines be put in motion they will cause the cones b b to turn the smaller wheels 
eg, fh, in opposite directions; but the pressure necessary to produce contact will be 
principally exerted between the cylinders g and h, which, being a rolling motion, 
is free from friction, and the power of the engine will thus be transmitted to 
the screw with only a loss of power entailed by the small amount of friction at 
k. It is obvious also in this contrivance that there is scarcely any friction at 
the bearings of i or j, which, owing to the cones having the force communicated at 
two opposite points in their periphery, exert no pressure on their bearings except 
that of gravity. 
The method of driving the screw may be stated to be almost the only hypo 
thetical part of this interesting subject. 
With such advantages as a screw propeller in certain cases obviously presents, 
some increased complexity we may be content to submit to; but it is contrary to 
the habits of British mechanics to rest satisfied with an acknowledged defect; and, 
judging from the mental resources of our engineers, by which greater difficulties 
have been overcome, we do not doubt but that an effective and simple method 
of communicating motion from the engine to the screw will be speedily supplied. 
We have enlarged our remarks upon the screw to an extent beyond what 
was originally intended, though probably not more than the importance of