Old Houses are full of Charactor. Unfortunatly a sloping floor in not the most desireable of those qualities.
There are many reasons for this, the most common seems to be rot from the bottom up.
If the post base was set under the floor slab you would never suspect that is has slowly subsided by several inches over the years.
Fortunately there is a fairly simple simple solution.
Once accurate measurments and calcluations have been made to evalute the particular situation, a new footing and post can be engineered and installed.