But my father's mind took unfortunately a wrong turn in the investigation; running, like the hypercritick's, altogether upon the ringing of the bell and the rap upon the door, --measuring their distance, and keeping his mind so intent upon the operation as to have power to think of nothing else, ----common-place infirmity of the greatest mathematicians! 
But my father's mind took unfortunately a wrong turn; running upon his ringing of the bell and the rap upon the door, measuring the distance betwixt them, and able to think of nothing else.
