For the next two whole stages, no subject would go down, but the heavy blow he had sustain'd from the loss of a son, whom it seems he had fully reckon'd upon in his mind, and register'd down in his pocket-book, as a second staff for his old age, in case _Bobby_ should fail him. 
For the next few miles, his subject was the heavy blow he had sustained from the loss of a son, whom he had reckoned upon as a second staff for his old age, if Bobby should fail him. 