Find Washington Irving's A History of the Life and Voyages of Christopher Columbus, Volume 1 by clicking here.
It can be challenging to find an authoritative source for an definition or explanation of a complex topic. The library has many scholarly reference books and other resources available online that can help with that task.
You might try searching "confirmation bias" in the following library resources (Note: Search "confirmation bias" with the quotes, to keep these two words together as a phrase when searching.)
With this information, and having read Chapter V of Irving's text, you can begin to think about whether Irving has established that Columbus committed this mistake in his reasoning.