Final answer:
Without additional context or a specific reference to the source material, it is not possible to accurately determine the exact day a boy delivered letters signed by Barney Northrup.
Step-by-step explanation:
The question about when a boy delivered letters signed by Barney Northrup could be referencing a specific literary work where the character named Barney Northrup is involved. We don't have a direct source or context that could provide the exact date from the information given.
If the question is pertaining to a book or story, it would be helpful to review the text or provide additional context to give an accurate answer. Generally, without specific context, one cannot conclusively determine the date of such an event within a story or narrative