\section{Introduction}
The finite volume methods are considered now as classical 
techniques 
to solve conservative laws problems. It derived by integrating the
basic equations over a grid cell and construct discrete 
approximations for the resulting integral terms, which provides 
a very natural way to use unstructured meshes that conform to complex
geometries .
F.Hermeline \cite{HERM},  N.K.Madsen and R.W.Ziolkwski
\cite{MADSEN} proposed methods for the Maxwell 
equations which require a primary grid and a dual grid based on the
Delaunay-Voronoï meshes. These
techniques were also used by K.S.Yee (\cite{YEE2}, \cite{YEE3}) to
construct a hybrid scheme combining a finite difference and a
finite volume methods applied to the Maxwell system.
The main drawback of these methods is
the difficulty to find tridimensional mesh generators.
Others types of finite volume methods have also been investigated
(\cite{SHA}, \cite{AERO}),
%for unstructured grids  
where all the field vectors are located at the same points. These
methods use
an upwind scheme 
for the space approximation with a MUSCL technique to 
get a high order scheme,  
and a Runge-Kutta sheme for the time discretization. To avoid
confusion, we denote these
methods a MUSCL finite volume schemes. 
These methods give a good 
resolution, but they require a relatively important CPU time compared
to finite differences schemes (Yee's scheme for
example \cite{YEE} ). 
We propose here a more simple and economical finite volume method 
which is based on a centered space scheme and a \\ leapfrog scheme 
for the time discretization. This method is second order accurate, 
and has no 
numerical dissipation. We present in this paper some theoretical 
analysis of this finite volume scheme, and we give some numerical
experiments and comparisons with a MUSCL finite volume method.
