CHAPTER I

.--Of the Open Sky.

Sec. 1. The peculiar adaptation of the sky to the pleasing and teaching of man. 204 Sec. 2. The carelessness with which its lessons are received. 205 Sec. 3. The most essential of these lessons are the gentlest. 205 Sec. 4. Many of our ideas of sky altogether conventional. 205 Sec. 5. Nature, and essential qualities of the open blue. 206 Sec. 6. Its connection with clouds. 207 Sec. 7. Its exceeding depth. 207 Sec. 8. These qualities are especially given by modern masters. 207 Sec. 9. And by Claude. 208 Sec. 10. Total absence of them in Poussin. Physical errors in his general treatment of open sky. 208 Sec. 11. Errors of Cuyp in graduation of color. 209 Sec. 12. The exceeding value of the skies of the early Italian and Dutch schools. Their qualities are unattainable in modern times. 210 Sec. 13. Phenomena of visible sunbeams. Their nature and cause. 211 Sec. 14. They are only illuminated mist, and cannot appear when the sky is free from vapor, nor when it is without clouds. 211 Sec. 15. Erroneous tendency in the representation of such phenomena by the old masters. 212 Sec. 16. The ray which appears in the dazzled eye should not be represented. 213 Sec. 17. The practice of Turner. His keen perception of the more delicate phenomena of rays. 213 Sec. 18. The total absence of any evidence of such perception in the works of the old masters. 213 Sec. 19. Truth of the skies of modern drawings. 214 Sec. 20. Recapitulation. The best skies of the ancients are, in _quality_, inimitable, but in rendering of various truth, childish. 215

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