The basis of construction is given in [Fig. 68.], half of it only being drawn, in order that the eye may seize its lines easily.
Fig. 68.
Two squares (of the required size) are first drawn, one above the other, with a given vertical interval, A C, between them, and each is divided into eight parts by its diameters and diagonals. In these squares two circles are drawn; which are, therefore, of equal size, and one above the other. Two smaller circles, also of equal size, are drawn within these larger circles in the construction of the present problem; more may be necessary in some, none at all in others.
It will be seen that the portions of the diagonals and diameters of squares which are cut off between the circles represent radiating planes, occupying the position of the spokes of a wheel.
Now let the line A E B, [Fig. 69.], be the profile of the vase or cup to be drawn.
Inclose it in the rectangle C D, and if any portion of it is not curved, as A E, cut off the curved portion by the vertical line E F, so as to include it in the smaller rectangle F D.
[p90]
]Draw the rectangle A C B D in position, and upon it construct two squares, as they are constructed on the rectangle A C D in [Fig. 68.]; and complete the construction of [Fig. 68.], making the radius of its large outer circles equal to A D, and of its small inner circles equal to A E.
The planes which occupy the position of the wheel spokes will then each represent a rectangle of the size of F D. The construction is shown by the dotted lines in [Fig. 69.];
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