[40] A more complete description of isometric ellipses will be found in Inventing for Boys by the present author and published by Frederick A. Stokes Co., of New York.
Fig. 49c. the proportions of an isometric ellipse
Some Simple Aids to Drawing
How to Draw a Circle.
—Should you ever want to draw a circle and have no compasses at hand or should you want to draw a larger circle than you can with your compasses tie a bit of strong thread to a pin, make a loop in the string at whatever length you want the radius—that is half of the diameter of the circle—to be.
This done, drive the pin in at the point where you want the center of the circle, put the point of a lead pencil in the loop and move it around the pin, as shown at [A in Fig. 50], keeping the thread taut and a perfect circle, nearly, will result.
Fig. 50a. how to draw a circle with a thread