Make a loop in one end of a thread as before and tie the other end tightly to a large pin; wind the thread around the pin until all of it is on except the loop; push the pin through the paper on which you want to draw the spiral and into the drawing board as shown at B.

Next put the point of the pencil in the loop and move it around the pin just as you did in making the circle and you will find that you have drawn a very pretty geometrical spiral which is known as the spiral of Archimedes. It is so called because Archimedes was the first to explain that it was caused by a point moving with uniform angular speed and receding from the center at a constant rate.

Fig. 50B. How To Draw A Spiral With A Thread