SLIDE RULE. An instrument composed of
sliding scales, and used to perform certain
arithmetical calculations. The annexed figure
shows the Nestler rule. In using this scale for
multiplication the figure 1 on the slide is made
to coincide with one of the two factors on the
scale, the product then being found opposite
the other factor as read on the slide. In division
it is necessary merely to place the divisor
read on the slide above the dividend read on the
rule, and the quotient will be found on the rule
below 1 on the slide. For involution the numbers
on the upper scale of the rule are the
squares of the numbers on the lower scale, and
the cubes can be found by inverting the slide. The inverse of this gives the square and cube roots. On the reverse of the slide is a scale of sines and tangents, and a scale by the use of which logarithms may be found.