Practical engineering drawing and third angle projection, for students in scientific, technical and manual training schools and for ..draughtsmen .. . 1 1 1 2 3 4 ^t 67. In Fig. 34 we have a straight-line designusually called the Greek Fret, and giving thestudent his first illustration of the use of theshade line to bring a drawing out in reliefThe law of the construction will be evident onexamination of the numbered squares. Without eiatering into the theory of shadows at this point we may state briefly the shoj) rule for drawing shade lines, viz., right-hand and loiver. ] That is, of any i^a
Practical engineering drawing and third angle projection, for students in scientific, technical and manual training schools and for ..draughtsmen .. . 1 1 1 2 3 4 ^t 67. In Fig. 34 we have a straight-line designusually called the Greek Fret, and giving thestudent his first illustration of the use of theshade line to bring a drawing out in reliefThe law of the construction will be evident onexamination of the numbered squares. Without eiatering into the theory of shadows at this point we may state briefly the shoj) rule for drawing shade lines, viz., right-hand and loiver. ] That is, of any i^air of lines making the same turns together or representing the limit of the same flat surface, the right-hand line is the heavier if the pairis vertical, but the lower if they run horizontally; alwayssubject, however, to the proviso that the line of inter-section of two illumin-ated planes is never ashade line. 68. The conic sectioncalled the parabola fur-nishes another interesting exercise in i-uled lines, whenit is represented by its tangeiits as in Fig. 35. The angle CA Emay be assumed at pleasure, and on the finished drawing the numbers may. SECTION-LINING. —LIJ^E-SHA DING. 23 ^ig-. 3S- be omitted, being given here merely to show the law of construction. All the divisions are equal,and like numbers are joined. Some interesting mathematical properties of the curve will be found in Chapter V. 69. A pleasing design that will test the beginners skill is that of Fig. 36. It is suggestive ofa cobweb, and a skillful free-hand draughtsman could make it more realistic by adding the the 60° triangle for the heavy diagonalsand parallels to them; the T-rule for the hor-izontals. Pencil the diagonals first but ink themlast. 70. The even or flat effect of equidistantparallel lines is called line - tinting; or, if repre-senting an object that has been cut by a plane,as in Fig. 37, it is called section-lining. The section, strictly speaking, is the partactually in contact wit
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