M. PLANTÉ has found that the long process of “forming” his accumulators is shortened if they are warmed during charging. The temperature best for this purpose is between 70° and 80°, at which limit the opposing electromotive force is somewhat less than when cold, and the resistance a great deal less. He does not find it advantageous to exceed this limit. We venture to suggest that the reason is that at boiling-point the oxygen and hydrogen are evolved in normal conditions, no ozone being produced. The electromotive force of oxygen against hydrogen is less than that of peroxide of lead against metallic lead, and far less than that of ozone against “nascent” hydrogen.