THE MECHANISM OF BICYCLES. 
395 
obtain true running, i.e. with the least possible rubbing friction 
between the teeth, it is absolutely essential that the vertices of the 
cones of which the pitch surfaces of the bevel wheels form the frusta, 
should coincide at a single point. In all machines there is liability of 
the frame to get slightly distorted either by an accident or by exces¬ 
sive pressure, and in that case great friction and spreading away of 
the wheels would ensue. 
The Acatene Company assert that they can insure the necessary 
rigidity. 
I believe that one is apt to feel a tingling sensation through the 
legs owing to the engaging of the teeth, and no doubt the success of 
this machine will depend in a large measure upon the accuracy attained 
in the cutting of the teeth and upon their durability. 
The Quadrant machines fitted with Lloyd's cross roller gear re¬ 
semble somewhat the bevel gearing. Instead of a pair of bevel wheels 
at each end of the shaft there is a pair of wheels with pegs pro¬ 
jecting at right angles, and on the pegs are rollers of hard steel. See 
diagram 6r. 
It is claimed by the makers of this mechanism that all spreading 
away of the wheels is avoided and that the minimum of friction is 
reached. Whether this is correct or not, only exhaustive experiments 
carried out with working loads and velocities can prove, the spinning 
of the wheel free of the ground cannot be accepted as a test of the 
efficiency. 
Certainly with this machine the pressures in driving act in a direction 
normal to the road and this must be looked upon as a decided advan¬ 
tage. 
Changes of gear can be effected in a few minutes by putting differ¬ 
ent sized wheels on the back hub. 
There appears to be a general opinion that both the Acat&ne and 
the cross roller reply to the foot pressure in starting much more 
quickly than a chain geared machine. There is also less back lash. 
A point to be noticed in support of the Acatene and cross roller 
gears is in connection with the strain on the hind axle. 
In a chain machine the load due to the weight of the frame and the 
rider is increased considerably by the pull of the chain in hill climb¬ 
ing, this pull acting at right angles to the load pressure. In the other 
machines this increased pressure acts upwards, tends to lift the frame 
and rider, and so decreases the pressure instead of increasing it. In 
the cross roller gear this lifting movement is more nearly vertical than 
in the bevel gear. It must be confessed, however, that part of this 
saving is lost again at the crank shaft bearing. 
Turnbull's. —This form of mechanism is interesting to many of us not 
only from the ingenuity of the invention, but also from the fact that 
Mr. Turnbull, the inventor, lives not more than one hundred yards 
from the Arsenal gate. 
The machine is one of the class for which it is often claimed that 
extra power of leverage is obtained without the loss of speed. Mr. 
Turnbull, I am glad to say, admits that extra power is not obtained. 
