hen that the Patent Office classification is based upon
"art" in the strict sense in which the word may be said to be used in
section 4886, Revised Statutes, but not necessarily in the looser sense
of industries and trades. A proper maintenance of the distinction
between the word "arts" of the statute and the phrase "industrial arts"
used in the sense of industries and trades is essential to an effective
classification for the purposes of a patent office search. Similar
instruments have been patented in three different classes, because of
the statements that one was designed for cooling water, another for
heating water, another for sterilizing milk; in four different classes,
because of the statements that one apparatus was to separate solids from
the gases discharged from a metallurgical furnace, another to separate
carbon from the combustion gases of a steam-boiler furnace, another to
remove dust and tar from combustible gas, and another to saturate water
with carbon dioxid. Owing to the continuance of a classification based
largely on remote use, many applications come into the office setting
forth inventions of very general application which nevertheless have to
be classified more or less arbitrarily in one of several arts in which
they may be used but to which they are not limited.

_Function or effect as a basis._[6]--Means of the useful arts are
related in different degrees. Resemblances selected as bonds for a
number of inventions may be more or less close. It is axiomatic that
close resemblances should be preferred over looser ones for
classification purposes. Processes and instruments for performing
general operations, such as moving, cutting, molding, heating, treating
liquids with gases, assembling, etc., are more closely bonded than those
for effecting the diverse separate successive operations directed toward
complex special results, such as making shoes, buttons, nails, etc.
Means of the former sort perform an essentially unitary act--the
application of a single force, the taking advantage of a single property
of matter. Those of the latter sort require the application of several
different acts employing frequently a plurality of forces or taking
advantage of several properties of matter. In the former case,
classification can be based on what has been called function, in the
latter it cannot be based on function but can be based on what has been
called effect (or product).

Function is closely related t