Premise: I had the same peculiar aching feeling finishing this book of letters that I do at the end of her novels.

Hypothesis: This book of letters gave me the same aching feeling I get at the end of her novels.
Answer: yes

Premise: Neither Tripp's lawyers nor anyone else (even Tripp, though she might obviously remember what was on them--but she was not accessible to the press at this point) could have heard those tapes or briefed reporters about them.

Hypothesis: Tripp's lawyers couldn't hear the tapes because they were kept in a safe.
Answer: it is not possible to tell

Premise: A twenty-five pound gun set on a battery of the imposing castle above the town has fired a single shell.

Hypothesis: The heavy gun on the castle still remains to be shot.
Answer: no

Premise: He had even been able to pass his hand and arm completely through the sample.

Hypothesis: His entire arm had gone through the sample.
Answer: yes