Fig. 152.
A pair of compasses set even by this construction will not, however, be entirely accurate, because there will be some degree of error, even though it be in placing the compass points on the lines and on the points marked, hence it is necessary to step the compasses around the circle, and the best method of doing this is as follows: Commencing at a, [Fig. 152], we mark off continuously one from the other, and taking care to be very exact to place the compass point exactly coincident with the line of the circle, the points b, c, d, &c., continuing until we have marked half as many divisions as the circle is to contain, and arriving at e, starting again at a, we mark off similar divisions (one half of the total number), f, g, h, arriving at i, and the centre k, between the two lines e, i, will be the true position of the point diametrally opposite to point a, whence we started. These points are all marked inside the circle to keep them distinct from those subsequently marked.
Fig. 153.
Fig. 154.