I have a problem with this sentence "When Adubon was Painting was a time of major scientific inquiry " Why the second was exerted without subject?
But the second was does have a subject.
You should parse the sentence this way:
[When Adubon was Painting] was a time of major scientific inquiry.
In other words, the subject of the sentence is the subject phrase when Adubon was Painting, which, itself, contains the subject Adubon. Depending on how you look at it, the sentence contains two subjects, with one embedded inside the other.