the gaoler returned a few moments later with a pair of glasses and the usual copy of the letter which he proceeded to read to the prisoner.这里which是不是定于从句定letter？课文最后翻译是囚犯念信了，所以我怎么也不明白。

翻译如下狱卒重新登台，拿来一副眼镜以及平时使用的那封信，然后为哪囚犯念了起来。

哦，明白了。

关系代词做read的宾语，read sth to sb，定从发挥并列句作用