Over many a quaint and curious volume of forgotten lore—
The narrator is telling us they are partaking in extra curricular reading, specifically of lore, long forgotten suggests it may not be common knowledge, that perhaps sets up the idea that we lack the knowledge to accurately judge the truth of the matter at hand.
The fact that he is reading and feeling weak and weary suggests his reading is not of the jovial variety
The fact that he is reading at night confirms his troubled state or perhaps is the cause of it.
Also the fact that he is reading lore at midnight confirms the assertion that the midnight hour is meant to represent the supernatural
