individual cases however, its length may be made to
vary. The only peculiarity in its construction is at the head. Here,
instead of slanting, it is made square, and the slightly concave (from
side to side) board against which the back of the bather is to rest, is
fitted in afterwards. This is necessary, because it is very difficult to
make a wooden tub with a slanting back water-tight. If the length of
the tub from outside to outside is made to measure about five feet ten
inches, the back-rest fitted in at a proper slant will bring the inside
of the tub to about the right length for an average male adult. All
around the upper edge of the tub runs a wooden coping, which must not be
fastened down however until all the attachments for conducting the
current are _in situ_. Along that portion of the top of the tub where
required--and this will depend on the situation of the binding posts
presently to be mentioned--and underneath the coping, runs a groove for
the reception of the wires that are to connect the carbon electrodes on
the inside of the tub with the binding posts on the outside. This groove
is continued vertically along the inside of the back-rest and foot of
the tub respectively, to communicate at either end with the bed for the
reception of the carbon plates. These vertical grooves should at their
lower end be a little over 1/4 inch deep, in order to admit of the wires
being introduced beneath the carbons.

The face of the foot of the tub and that of the back-rest, should have
in their centres (from side to side) and commencing at about five inches
from the bottom of the tub, a bed for the reception of the carbons. The
dimensions of these receptacles must of course correspond to those of
the carbon plates to be employed as electrodes. Those which I use
measure 12x8" at the head, 8x6" at the foot of the tub. They are 1/4"
thick. They are placed so as to have their long diameter correspond to
the height of the tub. The bed which is to receive the carbon at the
head of the tub must be deeper than 1/4" on account of the concavity of
the back-rest.

In order to adapt a tub to individuals of different lengths, it will be
found advantageous to have two small vertical cleats on each side of the
tub, near the foot and bottom, for the reception of a foot-board, which
will practically shorten the tub and adapt it to persons of different
lengths. This board may conveniently be six inches wide, and should have
a number of pe