And further on, Welles also wrote this,
...catch the bright forms of departed friends in the white clouds which wave over the moon.Welles wanted a correspondence between the imagined spiritual perceptions and physical Nature which provided "the standard of perceptible truth."
The constant action of thought in retirement, adds another charm to it. The mind here is not left merely to its own operation, reasoning on subjects of its own suggestion, without the standard of perceptible truth for the conclusion of such abstractions.
Seeing "departed friends in the white clouds" is definitely an example of pareidolia. Benjamin Welles, who was with Allston in Paris during the period when Allston painted Rising of a Thunderstorm at Sea, went back to Boston and wrote that people should look at nature with the intention of seeing what is now defined by the word pareidolia.