time, moreover, in
trying to bring within the four corners of his definition some uses of
the terms of beauty, which are really only applied to objects by way of
analogy, and are not meant to predicate the beautiful in any literal or
scientific sense.

[60] _Oeuv._, x.

There is no more interesting department of aesthetic inquiry than the
relations of the arts to one another, and the nature of the
delimitations of the provinces of poetry, painting, sculpture, music.
Diderot, from the very beginning of his career, had turned his thoughts
to this intricate subject. In his letter on Deaf Mutes (1751) he had
stated the problem--to collect the common beauties of poetry, painting,
and music; to show their analogies; to explain how the poet, the
painter, and the musician render the same image; to seize the fugitive
emblems of their expression. Why should a situation that is admirable in
a poem become ridiculous in a painting?[61] For instance, what is it
that prevents a painter from reproducing the moment when Neptune raises
his head above the tossing waters, as he is represented in Virgil:

Interea magno misceri murmure pontum.
Emissamque hiemem sensit Neptunus, et imis
Stagna refusa vadis; graviter commotus, et alto
Prospiciens, summa placidum caput extulit unda.

[61] It is to be observed also that he shows true perspicacity in
connecting the difficulty of transforming a poetic into a pictorial
description, with the kindred difficulty of translating a finished
poem in one language into another language. See also xi. 107.

Diderot's answer to the question is an anticipation of the main position
of the famous little book which appeared fifteen years afterwards, and
which has been well described as the Organum of aesthetic cultivation. In
_Laocooen_ Lessing contends against Spence, the author of _Polymetis_
against Caylus, and others of his contemporaries, that poetry and
painting are divided from one another in aim, in effects, in reach, by
the limits set upon each by the nature of its own material.[62] So
Diderot says that the painter could not seize the Virgilian moment,
because a body that is partially immersed in water is disfigured by an
effect of refraction, which a faithful painter would be bound to
reproduce; because the image of the body could not be seen
transparently through the stormy waters, and therefore the god would
have the appearance of being decapitated; beca