Electrostatic Storage Ring

In the trial \cite{BNL} of measuring the proton electric moment, storage rings with electrostatic lattice have been considered. Here an overview is given about the main parameters regarding such a kind of focusing. Beyond confirming all the issues regarding this subject, a non-null element $M_{31}$ is introduced in all the $3\times 3$ matrices which deal with the vector $(x,x^{\mathrm{\prime }},\mathrm{\Delta }p\mathrm{/}p)$ and its role is discussed.