98 FERGUSON'S LECTURES. 



LECT. sustain as much more friction, and consequently wear 

 ^J^- out as much sooner, than the hind-axle, as the fore- 

 wheels are less than the hind ones. But the great mis- 

 fortune is, that all the carriers to a man do obstinate- 

 ly persist, against the clearest reason and demonstration, 

 in putting the heavier part of the load upon the fore- 

 axle of the wagon; which not only makes the friction 

 greatest where it ought to be least, but also presseth the 

 fore-wheels deeper into the ground than the hind-wheels, 

 notwithstanding the fore-wheels, being less than the hind- 

 ones, are with so much the greater difficulty drawn out 

 of a hole or over an obstacle-, even supposing the weights 

 on their axles were equal. For the difficulty, with equal 

 weights, will be as the depth of the hole or height of the 

 obstacle is to the semi-diameter of the wheel. Thus, if 

 we suppose the small wheel D of the wagon A B to fell 



into a hole of the depth E F, which is equal to the semi- 

 diameter of the wheel, and the wagon to be drawn ho- 

 rizontally along ; and it, is evident that the point E of 

 the small wheel will be drawn directly against the top of 

 the hole ; and therefore, all the power of horses and men 

 will not be able to draw it out, unless the ground gives 

 way before it. Whereas, if the hind-wheel C falls into 

 such a hole, it sinks not near so deep in proportion to its 

 semi-diameter; and therefore, the point G of the large 

 wheel will not be drawn directly, but obliquely, against 

 th* top of the hole ; and so will be easily got out of it. 

 Add to this, that as a small wheel will often sink to the 

 bottom of a hole, in which a threat wheel will po but a 



