“As he is about to clasp her he feels a stunning blow upon the back of the neck; a blinding white light blazes all about him with a sound like the shock of a cannon--then all is darkness and silence!”
Up until this point in Section III, what readers have experienced is a hopeful fantasy where the noose around Farquhar’s neck brakes and he manages to escape to eventually make it back home to his wife. As he is about to hug her, reality catches up to him and he experiences his execution, and this is what the sentence above describes.
