s of the
work. This is a scale of reduction in _Degree_. There are two
Varieties in each degree; and they are marked with italic letters.

It may be shown, in tabular arrangement, thus:--

REALISM.............................................CONVENTIONALISM.

COMPLETE REALISM, in which all parts are represented, in
proper colors, and perfect gradation, with correct light and
shade (see Sec. 10).

FIRST DEGREE OF CONVENTIONALISM, in which all parts are
represented: (a) By a reduced number of Pigments, the other
qualities remaining; (b) By reduction in gradation and
shading to Flat-tints of several pigments (see Sec. 15).

SECOND DEGREE OF CONVENTIONALISM, in which all parts are
represented: (c) By a reduction to Monochrome of color, with
Gradation (_only_) remaining; (d) By reduction to Monochrome
of White and Black, with Gradation (_only_) remaining (see Sec.
16).

THIRD DEGREE OF CONVENTIONALISM, in which all parts are
represented: (e) By reduction to a Flat-tint of one pigment
on a ground of another; (f) By reduction to a Flat-tint of
White on Black, or _vice versa_ (see Sec. 17).

ULTIMATE CONVENTIONALISM, in which all parts are
represented; (g) By reduction to Outline of several
pigments; (h) Reduction to Outline of one pigment (see Sec.18).

Inasmuch as Realism ceases so soon as any reduction in the three
qualities (of color, gradation, and shadow) is introduced; and the
treatment becomes more Conventional in each method after the
first--these are classified under the heading of CONVENTIONALISM.

[There is an analogous scale of reduction in Form, from the
Complete-relief of an isolated Statue to the Flatness of a
Floor-plate; but this does not belong to the present subject.]

* * * * *

THE CYCLOSTAT.

The various processes commonly employed for the observation of bodies
in motion (intermittent light or vision) greatly fatigue the observer,
and, as a general thing, give only images, that are difficult to
examine. We are going to show how Prof. Marc Thury, upon making
researches in a new direction, has succeeded in constructing an
apparatus that permits of the continuous observation of a body having
a rapid rotary motion. The principle of the method is of extreme
simplicity.

[Illustration: FIGS. 1, 2, AND 3.--DIAGRAMS EXPLANATORY OF THE
PRINC