60 
MESSES. W. DE LA EUE AND H. W. MtTLLEE ON THE 
ending in a V piece, underneath and parallel with it, which falls into one of three 
notches to hold it out of contact when the handle H is upright, as in fig. 3, or in 
contact to the right, or to the left as shown in fig 2. 
After the adjustment of the distance between the terminals of the discharger, fig. 1, 
the current was usually sent alternately so as to make the upper terminal positive or 
negative by means of the discharging key just described, so that the striking distance 
was obtained for the current in both directions ; on breaking contact with this key 
there is no fear of the voltaic arc continuing the current, as was found to be the case 
with the ordinary form of the doubly reversing keys as soon as the battery reached 
Fig. 4. 
4000 cells, because the double distance of B' to S' and S to B amounts to 2^ inches ; 
and it has been found that the arc will not extend after separation of the terminals 
to more than 1-| inch even when the battery consists of 8040 cells. 
All the wires leading from the batteries are 0'0625 (ygth) inch diameter, and are 
covered with a coating of gutta percha 0 - 1 2 5 (-g-th) inch thick ; the wires as they run 
round the laboratory are supported on ebonite supports in order, as far as possible, to 
prevent leakage. The batteries are arranged in cabinets standiug on ebonite feet 
(E, fig, 4), and each tray of 20 also stands on ebonite feet. 
