,
_Depth_.

Group B. (Linear): _Linking Continuity_.

Group C. (Kinetic): _Rhythm_, _Intensity_, _Reaction_, _Key_,
_Culmination_.

Group D. (Static): _Grace_, _Balance_, _Harmony_.

This is a rough classification, for an opera does not necessarily
compare with a square rood of paint or a novel of Tolstoyan length;
indeed, on the volumetric basis, an opera may have less bulk than a
sonnet.

Group A. (Volumetric). By _concentration_ we mean the quality of
conveying a great deal within a small space. It follows that
_concentration_ is in inverse ratio to area, though it does not follow
that area is in inverse ratio to _concentration_. While _Anna Karenin_
is an enormous novel it is as concentrated as the sonnet of d'Arvers; on
the other hand, Francis Thompson's _Arab Love Song_ is more concentrated
than the complete works of Mrs Barclay; while any Rubens is more
concentrated than a modern miniature, an intaglio may be more
concentrated than twenty square yards of Delacroix. We nullify areas,
therefore, and must lay down that the test of concentration is the
effect: if the painter realises that the author has felt all he wrote,
if the writer sees that every line was necessary, then both can be sure
that they are respectively in presence of concentrated works.

Likewise with _relief_. A bas-relief may have none. A fresco may.
_Relief_ then is a matter of contrast, as is shown especially in the
mosaics of Taj Mahal; but its nature is easily seen if we compare prose
with paint:--

'He stood at the edge of the sea while the waves crept towards him,
nearer and nearer, sinuously flowing and ebbing, but ever nearer.
Ever.'

I give this as an instance, not as a fragment of literature. The lonely
'ever' gives _relief_ to the sentence of twenty-four words if we assume
that another long sentence follows. (If no sentence follows, 'ever' is
no longer _relief_ but _culmination_, see Group C.) The painter renders
the same effect by a more vivid line of foam in the middle distance,
the musician by interposing a treble motif between basses. Thus, if we
find variety of sentence, variety of tone, we have _relief_.

_Density_ and _Depth_ need not detain us long. Flaubert, the Psalms,
Jacob Epstein's _Oscar Wilde_, the Eroica and Velasquez all give the
sensation we call by those names; we mean by them that the work contains
a suggestion of something behind. Atmospheric quality, then, together