Leaving the port of Naples towards Sicily in 1777, the connoisseur Richard Payne Knight (1750-1824) narrated in his travel diary: “The infinite variety of tints were all harmonized together by that pearly hue, which is particular to that climate. (This tint very particularly marks Claude Lorraine’s Coloring). As we advanced into the open sea, the colours and forms seemed to sink into the Atmosphere and grow gradually indistinct, till at last the Sun withdrew its rays and left all in darkness.” Revealing the term ‘atmosphere’ in its literal meaning, Knight’s remark also, interestingly, hints at the fundamental role of optical theories and their interpretation in artistic practice in giving rise to the figurative essence of this same word. Encouraged by the national philosophical context, certain late eighteenth-century British landscapists aimed at conveying their personal impression felt upon observing the natural scenery, especially by handling color in travel sketches. Their Grand Tour became an artistic and aesthetical laboratory, into which they experimented with materials and processes in order to depict exotic landscapes with sensibility. Shared with the polite amateurs to whom these landscapes were destined, the specific training of these artists contributed to develop this sense of ‘atmosphere’, to be essentially rendered through pictorial effects. This paper demonstrates this pivotal turn in British landscape painting and the ideological as well as aesthetical evolutions it set forward.