C D, are the binding screws for attaching the external rheophores, C being con-
nected with i, D with d and d'. The latter are metallic atuds upon which e and /
ate made alternately to rest. A glance at the picture will show that the direction
of the current is changed through C D, according as the position of e and /, is
on d and c, or on c and d' respectively. (See A, B, C, in fig. 77}.
The see-saw mercury commutator may be used for stable bat-
teries; but has hitherto been mainly confined to the physiological
laboratory.
Current Altkrnator, Revekser, and Combiner.
L



The apparatus (fig. 76, 77) is made up of two reversers of the kind
just described fixed back to back on a tablet of wood. The one to
the right (i, 2, 3 in the Diagram) differs from the other in having
the two external studs (i, 3) prolonged into metallic bands so thai
when in the position depicted, the springs rest upon their inner
extremities. Two pairs of screws G, F, receive connecting wires
from the poles of the galvanic and faradic apparatus respectively.
When the springs rest upon i and 2 the galvanic current alone
circulates; when upon 2, and 3 the faradic. When upon i and
3 (as in the diagram) the galvanic current passes through 3 to
F— ; thence through the coil to F+, to 3, and finally reaches + or
+ (to which the electrodes are fixed) according to the position of



9^ current alteknator, kevrrssr, amd coubiner,

Fig. 76.
Fig. 77.
