such thing in nature as a perfectly defined outline; since the diffraction
of the rays, in passing it, causes them to be projected upon it more or
less, according to the nature of the particular body, and the intensity of
the light. And I may remark, by the way, that I believe this circumstance
of the projection of a star upon the moon's disc at the time of an
occultation, is to be accounted for on this principle (though with all due
deference to higher authority); a phenomenon which is to this day
unexplained.

Of course every outline is rendered less defined by any motion of the eye
of the observer, however slight. Hence, perhaps, the comparative
indistinctness of outline commonly seen in pictures, compared with those in
nature; as the artist {64} would be apt to take advantage of this
circumstance, and give to his painting the same kind of effect the reality
would have to an eye wandering over it; thereby taking away the attention
from individual parts, and, as it were, forcing it to judge of the general
effect, which general effect is, perhaps, the main object in painting.

Hence it follows that wherever, in any design, separate portions are
intended to arrest attention, the outline should be more defined and,
accordingly, we may remark that Albert Durer, and others like him, who were
very careful of minutiæ, are also distinct and hard in their outlines,
which is also the case, for the most part, in the Dutch school, and in
architectural paintings, fruit-pieces, &c.; and we find that in proportion
as the artist discards the comparatively unworthy minute accompaniments of
his subject, and aims at unity of effect, so does he neglect sharpness of
outline. Which is the _correct_ practice--distinctness, or indistinctness
of outline--will be differently judged by those who hold different opinions
on painting in general. While one person will maintain that a picture, to
be perfect, must be an exact copy of nature, in short an artistic