The mercury pumps now in use, whether those of Geissler, Alvergniat,
Toepler, or Sprengel, although possessed of considerable advantages, have
also serious defects. For instance, Geissler's pump requires a considerable
number of taps, that of Alvergniat and Toepler is very fragile in
consequence of its complicated system of tubes connected together, and that
of Sprengel is only suitable for certain purposes.

The new mercury pump constructed by Messrs. Greisser and Friedrichs, at
Stutzerbach, is remarkable for simplicity of construction and for the ease
with which it is manipulated, and also because it enables us to arrive at a
perfect vacuum.

The characteristic of this pump is, according to _La Lumiere Electrique_, a
tap of peculiar construction. It has two tubes placed obliquely in respect
to its axis, which, when we turn this tap 90 or 180 degrees, are brought
opposite one of the three openings in the body of the tap.

Thus the striæ that are formed between the hollowed-out parts of the tap do
not affect its tightness; and, besides, the turns of the tap have for their
principal positions 90 and 180 degrees, instead of 45 and 90 degrees, as in
Geissler's pump.

The working of the apparatus, which only requires the manipulation of a
single tap, is very simple. When the mercury is raised, the tap is turned
in such a manner that the surplus of the liquid can pass into the enlarged
appendage, a, placed above the tap, and communication is then cut off by
turning the tap to 90 degrees.

The mercury reservoir having descended, the bulb empties itself, and then