These dividers differ from the ordinary ones shown in figs. 169 and 170
in that they are provided with four steel points, one pair of which
being set to the full dimension will be reproduced by the other pair,
but in a smaller, or reduced size.
Fig. 171 are “bisecting” dividers, being proportional dividers, which,
when open, one end measures double the distance of the other.
Fig. 172 are proportional dividers; the points at one end are capable of
being changed, to measure practically any desired proportion at the
other end, by altering the position of the pivot where the legs cross
one another. The lower connecting link is a micrometer adjustment, for
minute measurements.
Fig. 173 are proportional dividers which are marked for the proportions
of lines and radii of circles, being provided with a rack movement for
adjustment.
Fig. 174 represents three-leg dividers, used for taking the position of
three points; this instrument is very useful in finding the position of
a point in a figure.
[Illustration: Fig. 171.--Fig. 172.--Fig. 173.--Fig. 174.]
[Illustration: Fig. 175.--Fig. 176.--Fig. 177.--Fig. 178.--Fig. 179.]