OF DRAWING.

When a man who is running wants to neutralise the impetus that
carries him on he prepares a contrary impetus which is generated by
his hanging backwards. This can be proved, since, if the impetus
carries a moving body with a momentum equal to 4 and the moving body
wants to turn and fall back with a momentum of 4, then one momentum
neutralises the other contrary one, and the impetus is neutralised.

Of walking up and down (375-379)