[Footnote 1:  Leonardo da Vinci, Treatise on Painting, paragraph 178.]

And again, in paragraph 176 of his treatise, Leonardo writes:  “The knowledge of the outline is of most consequence, and yet may be acquired to great certainty by dint of study; as the outlines of the human figure, particularly those which do not bend, are invariably the same.  But the knowledge of the situation, quality and quantity of shadows, being infinite, requires the most extensive study.”

The outlines of the human figure are “invariably the same”?  What does this mean?  From the visual point of view we know that the space occupied by figures in the field of our vision is by no means “invariably the same,” but of great variety.  So it cannot be the visual appearance he is speaking about.  It can only refer to the mental idea of the shape of the members of the human figure.  The remark “particularly those that do not bend” shows this also, for when the body is bent up even the mental idea of its form must be altered.  There is no hint yet of vision being exploited for itself, but only in so far as it yielded material to stimulate this mental idea of the exterior world.

[Illustration:  Plate IX.

STUDY BY WATTEAU

From an original drawing in the collection of Charles Ricketts and Charles Shannon.]

All through the work of the men who used this light and shade (or chiaroscuro, as it was called) the outline basis remained.  Leonardo, Raphael, Michael Angelo, Titian, and the Venetians were all faithful to it as the means of holding their pictures together; although the Venetians, by fusing the edges of their outline masses, got very near the visual method to be introduced later by Velazquez.

In this way, little by little, starting from a basis of simple outline forms, art grew up, each new detail of visual appearance discovered adding, as it were, another instrument to the orchestra at the disposal of the artist, enabling him to add to the somewhat crude directness and simplicity of the early work the graces and refinements of the more complex work, making the problem of composition more difficult but increasing the range of its expression.

But these additions to the visual formula used by artists was not all gain; the simplicity of the means at the disposal of a Botticelli gives an innocence and imaginative appeal to his work that it is difficult to think of preserving with the more complete visual realisation of later schools.  When the realisation of actual appearance is most complete, the mind is liable to be led away by side issues connected with the things represented, instead of seeing the emotional intentions of the artist expressed through them.  The mind is apt to leave the picture and looking, as it were, not at it but through it, to pursue a train of thought associated with the objects represented as real objects, but alien to the artistic intention of the picture.  There is nothing in these early formulae to disturb the contemplation of the emotional appeal of pure form and colour.  To those who approach a picture with the idea that the representation of nature, the “making it look like the real thing,” is the sole object of painting, how strange must be the appearance of such pictures as Botticelli’s.