“To bring a carriage into a different course from a straight one requires a circular motion, and at half a turn a carriage has established itself in a right angle to its position when at rest. “A two-wheeled vehicle turns on one wheel, which forms the centre at the place where it touches the ground, and the opposite wheel forms the circle struck from the said centre. The body in this instance follows the circular motion exactly as the axle, and consequently maintains a steady position above the wheels. “A four-wheeled vehicle remains in a straight line when first the front pair of wheels are turned under, then by the effect of the draught the hind pair of wheels follow in a wider circle. To effect a turning we bring the front axle first in a corresponding direction with the desired turn. “We make distinction between the moment of turning, or the angular position of the axles previous to the turning itself, and the effected turning of a vehicle round a centre or king bolt, according to the construction of the carriage part. The wheels have to be brought in a position corresponding with the direction of the turning. The body must be fully supported after the turning, and the front or dickey of a carriage must stand in a right angle to fore axletree. “We have to consider a few points relative to the height of the front wheel, and the elevation of the body above the ground, which averages 30 inches. To give a front wheel its proper height (between 3 feet 4 inches and 3 feet 6 inches) and have it turn a full circle, we sweep the body at the required place, viz. put in the wheel house of a proportioned length, and a depth between 3 and 4½ inches. “The front carriage part is fastened round the king bolt, turning that part horizontal. This action causes the front wheel to describe a circle, whose diameter is the width of the track; but as the wheel leans over at the top through the dish, we have a larger circle in the middle and top of the wheel. We, therefore, first find a top circle, having a diameter equal to the width between the highest point of the wheel, and a side circle following the termination of the cross diameter of the wheel, having as a centre the king bolt.” [Illustration: Fig. 28.]