THE MECHANISM OE BICYCLES. 
397 
pressure does not act in a direction tangential to the rotation of the 
sprocket wheel except when the pedal is horizontal and therefore it is 
not 0 A which appears at first sight to be the lever, but 0 D. 1 
By drawing the combination of levers to scale in seven positions, i.e. 
with crank vertically up and down, horizontal and in four positions 
midway between them I found the power gained with a 10" sprocket 
wheel was 
( 1 .) 
(3.) 
(5.) 
(7.) 
A 
A 
5 
12 
5 
X-X 
( 2 .) 
(4.) 
( 6 .) 
A 
A 
which gives an average of Ax j the denominator, however must be 
multiplied by f in order to compare it with the ordinary chain gear 
and the result will be that the same mean average A is obtained in 
each case. 
The inventor can, however, claim that the title “ Power Utilizing 
Gear ” is not inappropriate, for what the mechanism does is this : it 
varies the leverage according to the position of the pedal. It has 
already been seen that the greatest effective pressure from the foot is 
when the crank has moved down about 90° (see figure on page 396) 
and here we get the greatest leverage. 
Whether this varying leverage gives any real practical advantage 
to the rider only personal experience of a trial can tell, but it appears 
to me to be doubtful whether it is wise to sacrifice leverage just when 
the pedal is moving over the dead positions, especially when the 
resistances due to hill climbing and wind are in operation against one. 
Where the greatest leverage is given is the very point where the 
pressure of the foot is applied with the greatest advantage and there¬ 
fore the extra leverage is not required. I should be inclined to favour 
more the extra leverage being given when the pedal was passing over 
the dead points. But speaking generally on the subject of varying 
leverages, it must be remembered that for equally geared machines 
the mean leverage must be the same. What is gained at one point is 
lost at another and what is required is to so adjust the leverage 
that it is best suited to the power that can be applied by the rider. 
In the Elliptic gear, the sun and planet wheel arrangement takes 
the place of the sprocket wheels and chains, the sun wheel being keyed 
to the driving wheel, while the planet wheel is rigidly attached to the 
end of a crank arm (for there is another crank on the other side) 
pivotted at the centre of the driving wheel. The ends of the 
cranks are rotated by the action of the two long bent levers, 
the fulcra of which are moveable as they swing through the arc des¬ 
cribed by two rods suspended from the frame. Owing to the well 
known peculiarity of the “ sun and planet wheel ” motion (invented by 
Watt in 1781 when he found himself forestalled in taking out a patent 
for the “ crank and connecting rod ”) in order to get two revolutions 
out of the sun wheel for one of the crank, both sun and planet must 
have the same number of teeth—to get three revolutions the planet 
must have twice the number of teeth as the sun. By the arrange- 
1 These letters refer to a diagram drawn on the black board. 
