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section at right angles to the axis of either is a circle for the right cylinder, and an ellipse for the oblique one. This difference in cross- section, it may interest the student to know, is the reason why all cir- cular vessels or pipes intended to withstand an internal pressure when in use, are right cylinders, while those employed as mere conduits for the passage of air, smoke, or light gases, not under pressure, may be made in whole or in part of oblique cylinders. The solution of the fol- lowing problem will show how the development of the surface of an oblique cylinder is found. Problem 96 (Fig. 199). To find the development of the surface of anoblique cylinder of a given diameter and length, and hctvi ny its axis inclined at a given angle. Let the inclination of the axis of the cylinder be 60 ; then to find the development of its surface, we must first draw its elevation. Assuming it to be resting on one of its ends on a horizontal plane, take the IL as that plane, and at any convenient point in it, as a in No. 1, Fig. 199, draw a line making with the IL an angle of 60. With a as centre, and half of the intended diameter of the base of the cylinder as radius, describe a semi-circle cutting the IL in b and c ; and through those points draw lines parallel to a a'. On the axial line, set off from a the intended length of the cylinder, and through the point thus given, draw the line d c parallel to b c ; then d bee will be the elevation of the cylinder. Next, divide the semi-circle into any number say eight of equal parts, and through each point of division draw a line perpendicular to be to cut b c in the points 1, 2, 3, etc.; and through these draw 202