  The classical approach in finance attempts to model the term structure of
interest rates using specified stochastic processes and the no arbitrage
argument. Up to now, no universally accepted theory has been obtained for the
description of experimental data. We have chosen a more phenomenological
approach. It is based on results obtained some twenty years ago by physicists,
results which show that Pad\'e Approximants are very suitable for approximating
large classes of functions in a very precise and coherent way. In this paper,
we have chosen to compare Pad\'e Approximants with very low indices with the
experimental densities of interest rates variations. We have shown that the
data published by the Federal Reserve System in the United States are very well
reproduced with two parameters only. These parameters are rather simple
functions of the lag and of the maturity and are directly related to the
moments of the distributions.
