12 THE BOOK OF GARDENING. 



abscissa ba, keeping it in mind. Going forward to a, he has 

 the peg e inserted, reproducing in dc the length of the abscissa 

 ba, and so on. Irregular curves, with several centres, are those 

 which occur most frequently in tracing a garden ; they are also 

 traced by dieminement, as just explained. 



Fig. 6. — Tracing a Contra-curve. 



Fig. 5 represents a parabolic curve equally divided. In 

 working gradually forward from c' to d' it will be seen that the 

 abscissa? e'e, ff, and g'g, gradually lengthen, and that the flatter 

 the curves the shorter they become. The operator, therefore, 

 as he proceeds, must remember these proportions. Contra- 

 curves (Fig. 6) very often occur in the tracing of alley's,, the 

 object being to get round an apparent or a real obstacle in the 

 formation of the ground, such as a rock, &c. In such a case 

 the gardener has to trace first one curve and then the other, 

 with the same proportions, taking care that no breach of the 

 line occurs at f. 



In tracing an alley it is usual to first insert pegs at a con- 

 siderable distance from each other ; say, every 6oft. Some workers 



Fig. 7.— Defective Junction of Alleys. 



trace first one side of the alley and then the other, but it is 

 preferable to trace the axis first, as it will afterwards be easier 

 to effect a harmonious junction of the different alleys. The axis 

 traced, it is usual to go over the work again, correcting the 

 defects. Two men take a rod, equal in length to the width of 



