STANDARD AXLE FOR VEHICLES. 89 



any, in heavy wagons with less width, makes the same area, 

 adding little, if any, to the weight of the body. There are 

 few carriages made for narrow tracks which do not spring 

 by the widening ; and it is a matter of common experience, 

 that carriages purchased in the city, and widened for our 

 country roads, are sprung in the axle in a short time. Con- 

 sider the difference in strength required in lengthening a 

 bar of iron strong enough for its ordinary, reasonable maxi- 

 mum capacity, from four feet eight inches to five feet five 

 inches. Carriage-building has become a science, as well as 

 a trade, and no waste of iron or material is allowed ; so that 

 what would be safe and proper in an axle of one width would 

 be unfit for one nine inches longer. Whether the difference 

 in strength is more than the proportional addition in length 

 is a mechanical question into which I will not enter. Al- 

 though a leverage of two feet may not give more than double 

 the power of a leverage of one foot, the additional power on 

 a sudden shock, strain, or blow, such as mounting a frozen 

 rut, is vastly increased ; and this consideration is enough for 

 our present purpose. 



Fourth, there is another advantage in a narrow axle, 

 growing out of the laws of physical forces. A narrow-tracked 

 vehicle runs much lighter to the animal than a wide one, be- 

 cause the leverage is not so far from the centre line of draught. 

 The jerking motion caused by the wheels of vehicles meet- 

 ing obstructions first on one side, then immediately on the 

 other, when passing over uneven surfaces, worries horses 

 more, with an ordinary weight, than to pull a heavy load 

 when the draught is equal on each side. It follows that the 

 wider the wheels are apart, the greater the leverage, and 

 consequently the harder the jerks and jams which horses 

 have to bear and overcome : in other words, the power 

 should be supplied " in the line of the best support," as a 

 recent writer has expressed it. The nearer the power is 

 applied in a line with the wheels, instead of a line between 

 the wheels, the easier the traction. Accordingly, our horse- 

 railway companies have found that their extra horse hitched 

 in a line of one of the wheels does more effectual work. 

 Under the same laws of traction, persons who have been in 

 the habit of driving narrow vehicles find that in sudden 

 attempts to turn out of a rut, or avoid an object, the car- 



