20 Mr. C. Vernon Boyg [March 7, 



together ; this combination is ready enough to go straight, but no amount 

 of encouragement by the steering wheel will induce it to go in any 

 other direction. 



Bearing these facts in mind it will not be difficult to follow the 

 development of the tricycle. It would seem impossible in the first 

 arrangement (that with two wheels opposite one another, and a third 

 or steering wheel before or behind between them) to drive both sides, 

 for the wheels must be able to turn at different speeds ; let, therefore, 

 one be free to go as it pleases, if the other only is driven, we have at 

 once a very common form of tricycle in which one wheel drives, one 

 steers, and one is idle. Machines of this class have many defects. The 

 feeble steering power, combined with their unsymmetrical driving, 

 render them altogether untrustworthy. If much power is applied to 

 the driver, which can only have its share of the weight upon it, it 

 slips on the ground : if the machine is quickly stopped, owing to the 

 small weight on the steering wheel it is apt to swing round and upset; 

 nevertheless, those who are content with pottering about on our wood 

 pavement and gravel roads find this class of machine answer their 

 purpose, and owing to its cheapness and simplicity they do not care 

 to get a better. The second arrangement of the model, in which 

 riders must have recognised the " Coventry rotary," is free from most of 

 the defects of the form just described : there is more weight on the 

 driver but not enough to prevent its being made to slip round ; there 

 are two steering wheels a long way apart with plenty of weight upon 

 them, so that the guiding power in this type of tricycle is all that 

 can be desired. 



Let me now return to the first arrangement, in which two parallel 

 wheels are opposite one another. If by any possibility both wheels 

 could be driven and yet be free to go at different speeds, then, there 

 being so large a weight on the drivers, they could not be made to slip ; 

 the driving being symmetrical most of the twisting strain would be 

 taken off the steering wheel and still the machine would be capable 

 of rolling round a curve with perfect freedom. 



All the methods of solving the problem of double driving come 

 under two heads, one depending on the action of a clutch and the 

 other on differential or balance gear. 



The clutch action being the simplest, I shall describe that first. 

 In going round a corner the inner wheel must lag behind or the outer 

 wheel must run ahead of the other ; as either wheel must be inner or 

 outer, according to the direction of the curve, each must be able to 

 lag behind or each must be able to run ahead. If both were able to 

 lag behind, the machine could not be driven forward and it would be 

 of little use ; if both were able to run ahead, the machine could not 

 be driven backwards, a matter of small importance. There is on the 

 table a large working model showing how a four-sided wheel is free 

 to revolve in a ring, but is instantly seized when turned the other 

 way owing to a jambiug action of one or more of four rollers. The 



