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few simple rules, we need not worry ourselves with intricate problems.

But there is one deduction to which we must pay attention.

Fig. 56.The Foreshortening of Curves and Arches

Every receding line or surface must necessarily be foreshortened.

What is foreshortening?

A coin seen upright and straight in front is a perfect circle; a coin seen lying down is a coin diminished and a coin foreshortened. In the first example the circle is complete. In