Not P but Moby-Dick (27)

[Mike Jing]

>From Chapter 46:

It might be that a long interval would elapse ere the White Whale was seen.
During that long interval Starbuck would ever be apt to fall into open
relapses of rebellion against his captain’s leadership, unless some
ordinary, prudential, circumstantial influences were brought to bear upon
him.

What does "ordinary" and "circumstantial" mean here? "prudential" seems
easy to understand.