application, (as _tone_, &c.,) into technical terms. _Line_
thus signifies the course or medium through which the eye is led from
one part of the picture to another. The indication of this course is
various and multiform, appertaining equally to shape, to color, and to
light and dark; in a word, to whatever attracts and keeps the eye in
motion. For the regulation of these lines there is no rule absolute,
except that they vary and unite; nor is the last strictly necessary,
it being sufficient if they so terminate that the transition from one
to another is made naturally, and without effort, by the imagination.
Nor can any laws be laid down as to their peculiar character: this
must depend on the nature of the subject.

In the wild and stormy scenes of Salvator Rosa, they break upon us
as with the angular flash of lightning; the eye is dashed up one
precipice only to be dashed down another; then, suddenly hurried to
the sky, it shoots up, almost in a direct line, to some sharp-edged
rock; whence pitched, as it were, into a sea of clouds, bellying with
circles, it partakes their motion, and seems to reel, to roll, and to
plunge with them into the depths of air.

If we pass from Salvator to Claude, we shall find a system of lines
totally different. Our first impression from Claude is that of perfect
_unity_, and this we have even before we are conscious of a
single image; as if, circumscribing his scenes by a magic circle, he
had imposed his own mood on all who entered it. The _spell_ then
opens ere it seems to have begun, acting upon us with a vague sense of
limitless expanse, yet so continuous, so gentle, so imperceptible in
its remotest gradations, as scarcely to be felt, till, combining
with unity, we find the feeling embodied in the complete image of
intellectual repose,--fulness and rest. The mind thus disposed, the