Practical engineering drawing and third angle projection, for students in scientific, technical and manual training schools and for ..draughtsmen .. . the proportion 0 A : 0 A ::6:360°, since the arc AG A must equalthe entire circumference of the cones base. The student can make a paper model ofthe cone and helix by cutting out a sector ofa circle, making allowance for an overlap on which to put the mucilage, as shown by the dottedlines 0y and yvz in the 66 THEORETICAL AND PRACTICAL GRAPHICS. The development of the conical helix is evidently the same kind of spiral as its orthographic
Practical engineering drawing and third angle projection, for students in scientific, technical and manual training schools and for ..draughtsmen .. . the proportion 0 A : 0 A ::6:360°, since the arc AG A must equalthe entire circumference of the cones base. The student can make a paper model ofthe cone and helix by cutting out a sector ofa circle, making allowance for an overlap on which to put the mucilage, as shown by the dottedlines 0y and yvz in the 66 THEORETICAL AND PRACTICAL GRAPHICS. The development of the conical helix is evidently the same kind of spiral as its orthographicprojection. PARALLEL CURVES. 192. A parallel curve is one whose points are at a constant normal distance from some othercurve. Parallel curves have not the same mathematical properties as those from which they arederived, except in the case of a circle; this can readily be seen from the cam fig-ure under the lastheading, in which a point, as S-^, of the true spiral, is located on a line from 0 which is by nomeans in the direction of the normal to the curve at S,, upon which lies the jjoint S^ of theparallel curve. E-ig-. lOS.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjec, booksubjectlettering
