In painting, the necessity for scientific information, empirical if not rational, is still more conspicuous.  What gives the grotesqueness of Chinese pictures, unless their utter disregard of the laws of appearances—­their absurd linear perspective, and their want of aerial perspective?  In what are the drawings of a child so faulty, if not in a similar absence of truth—­an absence arising, in great part, from ignorance of the way in which the aspects of things vary with the conditions?  Do but remember the books and lectures by which students are instructed; or consider the criticisms of Ruskin; or look at the doings of the Pre-Raffaelites; and you will see that progress in painting implies increasing knowledge of how effects in Nature are produced.  The most diligent observation, if unaided by science, fails to preserve from error.  Every painter will endorse the assertion that unless it is known what appearances must exist under given circumstances, they often will not be perceived; and to know what appearances must exist, is, in so far, to understand the science of appearances.  From want of science Mr. J. Lewis, careful painter as he is, casts the shadow of a lattice-window in sharply-defined lines upon an opposite wall; which he would not have done, had he been familiar with the phenomena of penumbrae.  From want of science, Mr. Rosetti, catching sight of a peculiar iridescence displayed by certain hairy surfaces under particular lights (an iridescence caused by the diffraction of light in passing the hairs), commits the error of showing this iridescence on surfaces and in positions where it could not occur.

To say that music, too, has need of scientific aid will cause still more surprise.  Yet it may be shown that music is but an idealisation of the natural language of emotion; and that consequently, music must be good or bad according as it conforms to the laws of this natural language.  The various inflections of voice which accompany feelings of different kinds and intensities, are the germs out of which music is developed.  It is demonstrable that these inflections and cadences are not accidental or arbitrary; but that they are determined by certain general principles of vital action; and that their expressiveness depends on this.  Whence it follows that musical phrases and the melodies built of them, can be effective only when they are in harmony with these general principles.  It is difficult here properly to illustrate this position.  But perhaps it will suffice to instance the swarms of worthless ballads that infest drawing-rooms, as compositions which science would forbid.  They sin against science by setting to music ideas that are not emotional enough to prompt musical expression; and they also sin against science by using musical phrases that have no natural relations to the ideas expressed:  even where these are emotional.  They are bad because they are untrue.  And to say they are untrue, is to say they are unscientific.