os. of useful lead. It will be
seen that to increase the thickness of the sheet of lead merely augments
the duration of the accumulator, without affecting its capacity or its
manner of charging and discharging. Nos. 1, 2, 3, and 4 may be placed in
vessels of stoneware, glass, or ebonite, or in boxes of pitch pine, painted
with three coats of gum lac and lined with sheet lead. Nos. 5 to 12 are
only sent out in pitch pine boxes lined with lead. The box is supported on
feet of porcelain of the shape of a mushroom. If a drop of water falls upon
this foot, it cannot give a communication with the earth, since, falling
upon the broad part of the mushroom, it will glide off without running
along the foot, which serves as the stalk of the mushroom. A slip of glass
is placed under each foot; the part which supports the mushroom is covered
with an insulating varnish, which prevents the formation of climbing salts
and preserves the screws from rust. A common layer of insulating varnish is
applied under the head of the mushroom.

As regards the advantages of the Montaud accumulator we notice, first, its
longevity. Dr. D'Arsonval points out that the accumulators of the Plante
class have a great advantage over the Faure type as regards duration, and
that the most striking quality of the Montaud accumulator is its longevity.
The inventor has in his possession positive plates, five to six years old,
completely peroxidized, though there remains in the interior a thin core of
metallic lead sufficient to give passage to the current. The adhesion of
the peroxide is such that to detach it, it must be beaten with a hammer
upon an anvil. The next four points--i.e., the rapidity of charge; the
yield, much greater than that of any other system in proportion to its
surface; its small weight in comparison with its yield; and its capacity,
which for an equal weight is greater than that of any other accumulator. In
his experiments in September, 1885, Dr. D'Arsonval obtained with an
accumulator of 2 square meters of surface:

Useful capacity 40 ampere hours.
Total 62 " "
Surface 2 square meters
Charge 10 amp. per sq. meter.
Discharge 20 " " "
Useful weight of lead 10 kilos.

Representing a total capacity of six ampere hours per kilo., and of a
discharge of 5 amperes per kilo., or a total capacity of 81 ampere hours
per square meter, and