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indeed. We should not require rotatory motion. The tail 
might be attached directly to the middle of a cylinder 
sliding backwards and forwards on a fixed piston-rod, the 
cylinder and piston-rod forming small ares of circles, the piston- 
rod being also the steam-pipe. 
(4) On a method of transforming rotutory motion into 
rectilinear, so that the rotatory motion remaining 
constant the rectilinear may be completely controlled 
and made to vary as to speed—may be stopped or 
reversed at pleasure. By J.C. W. Enis, M.A. 
Two equal cones with their vertices fixed together forming 
a double cone have a common axis. On this same axis there 
are two other cones with their bases fixed together so that they 
form another double cone. All these cones are formed of bars, 
so that the vertex of the first double cone can lie in the interior - 
of the second double cone. The axis is not attached to the first 
double cone, but is to the second, so that sliding the axis in 
direction of its length the position of the cones may be altered 
with regard to each other. The intersections of the cones form 
two wheels, the sum of whose radii is constant, but the radii 
may have any ratio to each other. 
An endless rope is passed over one of these wheels, round a 
distant moveable pulley A, wnder the other wheel, half round it, 
then round another moveable pulley B, and then wnder the first 
wheel. The two moveable pulleys may be connected by a rope 
passing over fixed pulleys. 
If the cones be now made to revolve and the double cones 
be placed symmetrically, the wheels they form will have equal — 
radii and the pulleys A and B will remain in their positions as 
the endless rope runs round. But if the common axis of the 
cones be made to slide, the radii of the wheels will alter and the 
pulley A can be made to approach or recede from the cones 
with any rapidity according to pleasure, without disturbing the 
