Ellsworth M. Longfield

“ The diagonals of a square, or rectangle, always divide each other into two equal parts. Using the point where the diagonals cross each other (intersect) as a center, draw a circle that will just touch the center of each side of the square. What is the diameter of this circle? How does this diameter compare with the length of the sides of the square? You have drawn what is known as an inscribed circle; that is, a circle whose circumference touches all sides of the containing figure but does not pass beyond the sides. What is the area of this square? ”

“ A chimney tube is a short piece of pipe intended to be built into a chimney. If the tube is held on a level with the eye, the sides, the top, and the bottom will appear as four straight lines. The elevation of Fig. 40 shows this view. It is impossible to tell whether this elevation represents a flat or a curved surface unless another view is drawn. For this reason a profile should be drawn. This profile will show that the elevation is that of a cylinder. Extension lines are used to locate this profile properly. Fig. 41. Three dimensions are given in the elevation. ”

“ All dimensions on the elevation and the patterns should be full size. These are known as Witness Dimensions, and the workman always follows these while manufacturing from scale drawings. The use of witness dimensions relieves the workman from responsibility for errors, transferring this responsibility to the draftsman or designer. ”