The depreciation of Salvator Rosa's clouds and skies is a continuing theme throughout Modern Painters I. On the 'rolling' clouds of Salvator Rosa see Reynolds in Discourse Thirteen, 1786:
Like the history painter, a painter of landskips in this style and with this conduct, sends the imagination back into antiquity; and, like the Poet he makes the elements sympathise with his subject: whether the clouds roll in volumes like those of Titian or Salvator Rosa, - or like those of Claude, are gilded with setting sun... All these circumstances contribute to the general character of the work, whether it be of the elegant or of the more sublime kind. ( Reynolds, Discourses, p. 237)
Ruskin appears to have this passage in mind at MP I:227, where he refers to the 'rolling' clouds of Salvator Rosa. Ruskin's 'imagination', unlike Reynolds 's, is sent not 'back into antiquity' but to the growth of steam-powered factories in the first half of the nineteenth century.
Elsewhere clouds which Ruskin takes to be by Rosa are cauliflower-like in No. 220 of the Dulwich Gallery, and defy the laws of nature in Number 159 of the Dulwich Gallery. Like the water of Canaletto, the clouds of Rosa are treated mechanically.
In Modern Painters V ( Works, 7.161) Salvator Rosa, in his treatment of clouds, is joined with Claude, Ruisdael and Wouwerman as one of those who, unlike Turner, 'chooses never to look for them - never to pourtray'.