top, of the same copper as the sides and bottom, is depressed conically.
like a hopper, and wired at its outer edge, forming a lip all around for
pouring out of. The central cell is connected with the outer case only
by three rings of hard rubber (vulcanite), each 0.25 inch thick, the
middle ring completely insulating the cell from its continuation upward,
and from the outer case. A narrow flange is turned outward at the upper
edge of the cell, and a similar flange is also turned outward at the
lower edge of the cylindrical continuation of the walls of the cell
upward. Between these two flanges, the middle ring of hard rubber is
interposed, and the two parts, the cell and its upward continuation,
are clamped together by the upper and lower rings of hard rubber, which
embrace the flanges and are held together by screws. The joints between
the flanges and the middle ring of hard rubber, which might otherwise
leak a little, are made tight with asphaltum varnish.

[Illustration: Fig. 1.]

Fig 1 shows two partitions, dividing the space between the cell and the
case into three compartments, and a concave false bottom. The cover is
also seen to be divided into three compartments, by two partitions, and
each compartment of the vessel and of its cover is provided with a small
tube for inserting a thermometer. This construction was adopted in the
first instruments made, for the purpose of observing the rate of heat
transmission through the successive compartments, but these parts are
without importance with respect to the practical use of the instrument,
and may as well be omitted, as they considerably increase the cost,
being nickel-plated and polished on both sides. The top and bottom
plates of the cover are of 0.01 inch brass, nickel-plated and polished
on both sides, both convex outward, the bottom plate but slightly, the
top plate to 4.25 inches radius. A ring of hard rubber connects, yet