Cloud perspective: rectilinear (2)

From Modern Painters V, Plate 64 in John Ruskin, Works Vol. VII, ed. by Cook and Wedderburn (London: George Allen, 1905), p. 152.

One of a series of cloud perspective diagrams used by Ruskin in his final volume of Modern Painters (1860), in the chapter titled ‘The Cloud Flocks’, ‘Cloud Perspective: Rectilinear’ illustrates the application of perspective to the representation of cloud forms.
In the three figures, the viewpoint is that of an observer facing the cloud formations, which – as a conventional landscape painting – are boundaried by a rectangular frame. He writes, ‘Supposing that the breadth included was one-fourth of the horizon, the shaded portions … represent square fields of clouds, and those in the upper-most figure narrow triangles … In each figure, the shaded portions show the perspective limits of cloud-masses, which, in reality, are arranged in perfectly straight lines, are all similar, and are all equidistant from each other.’ (LE 7 (1905)/153).
Ruskin acknowledges the limitations of the ‘Rectilinear’ perspective, because he understood the skies as a complex system impacted by other atmospheric phenomena: wind, mist, or pollution. ‘Cloud Perspective: Rectilinear’ is followed by a paired diagram, ‘Cloud Perspective: Curvilinear’, which applies geometric compositional rulings to the natural curvature of cloud formations.
In inviting his readers to pay attention to clouds, Ruskin offered a bridge between new scientific knowledge, and new forms of visual representation: 'attention to the real form of clouds, and careful drawing of effects of mist; [...] that the appearance of objects, as seen through it, becomes a subject of science with us; and the faithful representation of that appearance is made of primal importance, under the name of aerial perspective' (LE 5 (1904)/317). Against flatness, Ruskin’s technical drawings insist on a mode of reading the skies that accounts for the flux of atmospheric elements.
The project that became the five volumes of Modern Painters began as a defence of the landscape artist J. M. W. Turner. In Modern Painters I (1843), Ruskin describes Turner’s skies: ‘It is a painting of the air, something into which you can see, through the parts which are near you, into those which are far off; something which has no surface, and through which we can plunge far and farther, and without stay or end, into the profundity of space’ (LE 3 (1903)/348).