392 
THE MECHANISM OF BICYCLES. 
i.e.j it has saw¬ 
shaped teeth pro- 
jecting inside, 
while the hub has 
attached to it 
four small pawls, 
the ends of which 
are kept pressed 
against the an¬ 
nular wheel by 
light springs so 
that it is only 
when the pedals 
are being worked 
with a forward 
movement that 
the sprocket 
wheel drives the 
hub and conse¬ 
quently when the 
pedals are kept stationary the wheel can still run on, the 
pawls merely slipping over the teeth. This is known as a “ free 
wheel 99 arrangement. In the machine before us the large sprocket 
wheel has 18 teeth and the smaller one 8, consequently with a 28" 
wheel it is geared to 63. The large sprocket wheel is made in two 
portions in such a way that by a back pressure upon the pedals the 
two portions expand, and although no fresh teeth come into play 
(except that one tooth becomes two teeth) the perimeter of the wheel 
is lengthened a distance equal to the pitch of either one, two, or three 
teeth with a consequent change of gear of 63-66-70 or 73. 
The sprocket wheel at its smallest, i.e., 18 teeth is slightly oval, 
with 19 teeth, a circle and with the equivalent of 20 and 21 teeth an 
oval. When the sprocket wheel is elliptic in shape the foot will not 
have an even velocity of rotation. This is stated by some to be a 
serious drawback, others who have ridden the machines maintain that 
not only is no inconvenience caused but it is difficult even to detect 
the irregularity. 
To obviate the difficulty caused by the slackness of the chain at the 
smaller gears, a small sprocket pinion of celluloid is kept pressed 
down by a light spring against the lower return of the chain. This is 
a disadvantage, as obviously extra friction and vibration must be 
introduced. 
Only a practical trial, extending over a long period, can prove 
whether this and many of the other forms of mechanism brought to 
notice give satisfactory results as regards the friction, vibration, wear 
and tear of parts and power to withstand the action of the mud, rain 
and dirt. 
Personally I am very much opposed to a free wheel attachment, 
owing to the power of back pedalling being taken away. I feel sure 
j Protean, 
