ample, above, division has been effected on the one basis of form or
contour. If it had been desired to separate also on material, for
example, if it were deemed important to locate all brass scrap, each of
the groups based upon form could be divided into one of _brass_ and one
_not brass_, or the entire heap could be divided into _brass_ and _not
brass_, and under the heading "brass" could be indented the various
articles made of brass, and under "not brass" the various articles not
made of brass, and this would double the number of divisions. If also it
were desired to separate the lead articles in the same manner the number
of classes would be tripled. But, as in the book illustration, it may be
impracticable thus to multiply subdivisions, and the basis "form" having
been selected as of _first-rank_ importance, all divisions based upon
form should be completed and kept together. Then, "material," having
been selected as of _second-rank_ importance, should be carried out with
respect to all objects in which form is non-essential. If enough brass
balls were found to render it advisable to make a subdivision of them,
they should be assembled into a subclass indented under "balls" and not
into a subclass indented under "brass." Having selected one basis as
_primary_, it should never subsequently be made _secondary_ or _vice
versa_. Some such restriction on modes of division appears salutary in a
system of divisions designed to definitely limit search. The arrangement
herein sought to be explained is susceptible of use to limit all
searches for a single definitely stated invention to a subclass properly
entitled to receive it or those indented under it, and to those
subclasses above, which may include it as a part of an organization or
specialized means.

As between coordinate groups divided on the same basis, there is no
question of superiority and inferiority. The terms "superior" and
"inferior" are useful in questions of relationship between combinations
and subcombinations or elements thereof, and between groups founded on
effect or product and those founded on simple function. The mere
difference in complexity of mutually exclusive coordinate groups
involves no relationship of superiority or inferiority. A subclass to
receive a screw-cutting lathe is superior to a subclass to receive a
lathe-headstock, a locomotive class is superior to a class to receive
steam-engines, for the reason that the lathe is a whole of which