CH. XIV TURNING AND BACKING 343 



In the movements thus described, the coach is 

 supposed to be put on the lock by one movement 

 of the front axle from a straight line, but in turning 

 into a curve from a straight line, until the constant 

 angle Q f the axles is reached, the hind wheels will 

 follow the front ones, not in a circle, but in a 

 curve called the ' tractrix,' because it results from 

 their being drawn by the front wheels by means 

 of the perch, and, on returning from a circle to a 

 straieht line, it will be some time after the front 

 wheels have taken the straight line before the hind 

 wheels will take it. The further apart the axles 

 are, the more marked this will be, and this is a 

 reason why a long geared carriage, like a landau, 

 runs harder than a short one, after making a turn, 

 the hind wheels coming into the straight line very 

 slowly. 



In backing movements, the mistake is usually 

 made of not turning the front wheels enough to 

 one side, and the coach does not, therefore, in its 

 movement, respond to the expectations of the 

 coachman. 



In driving up to a door, it may be desirable to 

 back into a positio'n closer to the kerb than could 

 be taken at first, owing to some obstacle's being in 

 the way, and it will be found, that unless a very 

 decided anele is made with the front wheels, the 

 result will be unsatisfactory and very little ground 

 will have been gained in the proper direction. 



Should there be an obstruction on the street at a 



