Gradually, landscape artists developed a new uncertainty as to whether the external world could be described objectively. Painters knew that no physical entity remains constant, least of all a landscape which is subject to the continual flux of changing weather and sunlight in the course of the day.

In the early 1860s, various progressive painters began to seek ways to suggest the fugitive nature of the landscape’s appearance. Even some who had previously painted in an exhaustively realist way now simplified, abstracted and generalised their representations. Frederic Leighton was one of many who looked for particular qualities of light, so that topography and architecture appear to be seen through veils. Even so, he believed the sketches he made were ‘accurate in the impression of the effect’.

Nonetheless, the legacy of Pre-Raphaelitism was still strong. Intensity and particularity of inspection characterised the work of the 1860s, as they had the 1850s. All of these types of work depended, as ever, on careful inspection, even when crystalline clarity had given way to atmospheric murkiness, and frozen instantaneity had been replaced with effects that slowly enveloped the landscape. They showed a generation’s obsession with the processes of optical observation.