Cube Root [Direct Method). — The method of extracting
the cube root of a number will be evident from the fore-
going explanation. Employing the same scales, the slide is



A PRACTICAL MANUAL. 41

mooed either to the right or left until under the given number orb
A is found a number on the l.h. B scale, identical with the
number simultaneously found on D under the right or left index
of C. This number is the required cube root. From
what has already been said regarding the combined use of
these scales in cubing, it will be evident that in extracting
the cube root of a number, it is necessary, in order ta
decide which scales are to be used, to know the number of
figures to be dealt with. It is therefore necessary (as in
the arithmetical method of extraction) to point off the given
number into sections of three figures each, commencing at
the decimal point, and proceeding to the left for numbers
greater than unity, and to the right for numbers less than
unity. Then if the first section of figures reading from the
left consists of —

1 figure, the number will evidently require to be taken
on what we have called the " units " scale — i.e., on the l.h.
scale of A, using the l.h. index of C.
If of 2 figures, the number will be taken on the " tens "'
scale — i.e., on the e.h. scale of A, using the l.h. index of C.
If of 3 figures, the number will be taken on the
"hundreds" scale — i.e., on the l.h. scale of A, using-
the R.H. index of C.
