longtable in LateX to wide?
===

I am having problems with a longtable, it goes off the side of the page and any attempt to limit the width only seems to work on the first page. here is a cut down version of my table 

    % Appendix B
    \chapter{Elelments for the MetDB Retrieval}
    \label{AppendixB}
    \lhead{Appendix B. \emph{Elelments for the MetDB Retrieval}}
    \chapter{Elelments for the MetDB Retrieval}
    \label{AppendixB}
    \lhead{Appendix B. \emph{Elelments for the MetDB Retrieval}}

    \begin{center}
    \begin{longtable}{|c|c|c|} %try definind the width here
    \hline
    \textbf{Element Name} & \textbf{Element Description} & \textbf{Units} \\
    \hline
    \endfirsthead
    \hline
    \textbf{Element Name} & \textbf{Element Description} & \textbf{Units} \\
    \hline
    \endhead
    \hline

    table entries...

    \hline
    %\end{tabular}
    \caption{Elelments for the metDB retrieval}
    \end{longtable}
    \end{center}

here is an image [https://www.dropbox.com/s/negmpy7cnk3ymqc/longtable.png][1]


  [1]: https://www.dropbox.com/s/negmpy7cnk3ymqc/longtable.png

any help on this subject would be nice! thank you!

Jason