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 12×8″ at the head, 8×6″ at the foot of the tub. They are ¼″ 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 ¼″ 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 perforations about an inch in diameter, for the transmission of the current to the feet. 1¼″ pine plank is the most suitable wood to use in the construction of the tub. This is preferable to any of the hard woods, because of the greater facility of fitting in the electrodes etc. It is also the most economical. (_b_) _The electrodes and connections._ These consist of two carbon plates, two brass binding posts, and insulated wires to connect the carbons with the binding posts, and these with the battery. The carbons are such as are ordinarily employed in the construction of galvanic batteries, and can, as well as the wire and binding posts, be procured from any house that deals in telegraph material. Their size is to some extent optional; the dimensions I have given above however answer very well. The inside of the tub having received one or preferably two coats of paint, the carbons are now fitted in the receptacles provided for them. The next step is the attaching of the binding posts. These should be of the kind known as “single” binding posts with “wood screws.” The most convenient location for them will be found on the coping covering the horizontal portion at the head of the tub. Here the coping, as it has to cover not only the upper edge of the head of the tub, but that of the back-rest also, is of necessity much wider than at any other portion, and thus affords most room for the binding posts. Having marked out then a site for the binding posts, say in the centre of the coping at the head of the tub—which should now be placed in position—and about two inches apart, the posts are laid aside to be put in place when the wires are all _in situ_, and the coping fastened down.