The essentials of descriptive geometry . 34. A line may be revolved into H or V about an axis whichHes in H or V by revolving any two of its points. The line and axis must, however, He inthe same plane else onepoint of the revolving linewould touch H or V beforethe other. Fig. 38 shows aline AB revolved into H atApiBh about MN whichhes in H and is parallel toAB. The location of thepoints Ah and Bh maybe found as indicated inArticle 32. 35. Either a point or aUne may be revolved aboutan axis into the plane of the axis when the plane does not coin-cide with the H or V but is parallel to H or V.
The essentials of descriptive geometry . 34. A line may be revolved into H or V about an axis whichHes in H or V by revolving any two of its points. The line and axis must, however, He inthe same plane else onepoint of the revolving linewould touch H or V beforethe other. Fig. 38 shows aline AB revolved into H atApiBh about MN whichhes in H and is parallel toAB. The location of thepoints Ah and Bh maybe found as indicated inArticle 32. 35. Either a point or aUne may be revolved aboutan axis into the plane of the axis when the plane does not coin-cide with the H or V but is parallel to H or V. The method by. REVOLUTION OF POINTS 41 which this may be done may be readily understood by con-sidering that a secondary H or V plane passes through the revolution, then, may be referred to this new H or V planeand may be accomplished as indicated in Article 32. Fig. 39 shows the plan and elevation of a line MN which isto be revolved into the plane of the axis PQ. The revolutionmay be accompKshed as indicated above or by working the Fig. 40. problem without the use of the secondary H or V plane. In thefigure the line MN has been revolved into the plane PQ directly,M falls at a point whose elevation is m, m being a distancefrom the axis equal to the hypotenuse of a triangle whose base isthe distance of m to the axis, or my, and whose altitude is thedistance M is from the plane of the axis, or mx. 36. To revolve a plane into H or V about the H or V a point on the trace, as A on the trace tT in Fig. 40, 42 ESSENTIALS OF DESCRIPTIVE GEOMETRY Revolve this point into H about tT as an
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