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revolution of a particular figure about an axis, it follows that a cross- section at right angles to its axis of any one of them will be a circle, while a section throng Ji its axis will be a similar figure to that of which its generator formed a half-part. An oblique section through the axis of all of them would be a figure of elliptic form, while one which did not cut the axis would partake of the form of its axial section. Under these circumstances, as the finding of any required section of one or all of them merely involves the application of methods of procedure already explained, it is unnecessary here to further elaborate them. All that is required by the student for the mastery of this part of our subject, is to thoroughly appreciate the exact form and mode of generation of the different solids enumerated. This attained, there will be no difficulty in the solution of any problem that may arise in connection with their projection. Before concluding this chapter, and with it the subject of the " Projection of Solids with Curved Surfaces," it will be necessary to show, how the principles explained in Chapter XL, on the " Lining-in of Drawings in Ink," are to be applied to representations of this class of solids. It has been shown in Chapter XL, that the projections of rays of light, in the direction they are assumed (in Mechanical drawing) to fall upon the object illumined, are parallel right lines in plan and elevation, making an equal angle of 45 with the intersecting line of the planes of projection. To determine then how to line-in the representation of a curved-surfaced solid, we have to find how the light falls upon it. Now to do this, let the circle cedb in No. 1, Fig. 156a, be the plan of a cylinder, and the rectangle ABCD No. 2 its elevation. Through