84 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
those observed with the same number of similar cells on subsequent 
Compare, for example — 
1200 cells. 2400 cells. 
XIV. 0-0058 0-0255 
XVIII. 0*00475 0-0200 
with the mean of XXIII., XXIV., XXV. 0'G1337 0"05G7 
occasions. 
By standing, as has been before stated, an oxychloride of zinc is formed on the 
surface of the zinc rods, and we have further noticed that the fluid in the cells 
becomes slightly alkaline ; it is possible, but not certain, that the EMF may be 
diminished in consequence of the alkalinity, and the striking distance influenced by 
the change.* But, on the other hand, when a second series of 2400 cells was charged 
up, on May 27 and 28, 1876, no such unusual length of spark was obtained ; hence we 
conclude that some special cause influenced the long discharge XXIII., XXIV., XXV., 
to be discovered by future experiment. A comparison of the numbers obtained when 
spherical or flat surfaces were used as terminals with those when a point and a disc or 
two points were used, will show that for low tensions the striking distance is fully 
as great, and in some cases greater, with spherical or flat terminals, than when one 
terminal was a point or when both were points. 
From the curves laid down on Plate 8, which represents the original plotting 
reduced to f ths in each direction, we have deduced the numbers given in Table XI. 
But, in the first instance, a mean curve was drawn for each of the irregular curves 
representing the actual observations ; these mean curves are not given in Plate 8, in 
order to avoid confusion. 
Table XI. — Showing the length of spark from the mean curves derived from those 
shown in Plate 8. 
1000 cells. 2000 cells. 3000 cells. 4000 cells. 5000 cells. 6000 cells. 7000 cells. 8000 cells. 
Curve. 
inch. 
inch. 
inch. 
inch. 
inch. 
inch. 
inch. 
inch. 
-XIII 
0-0057 
0 0220 
0-0540 
0-100 
0-160 
0-220 
0-283 
0-347 
XIV 
0 0050 
0-0195 
0-0550 
0-110 
0-173 
0-236 
0-298 
0-358 
XVI 
0 0030 
0-0200 
0-0567 
0-108 
0-169 
0-233 
0-299 
0-366 
XXVII 
0-0040 
0-0160 
0-0405 
0-082 
0137 
0-198 
0-264 
0 337 
XXII. Mean of XIX., XX., XXI. 
0-0080 
0-0330 
0-0710 
0-114 
0158 
XII. Mean 
0-0051 
0-0221 
0-0554 
0 103 
0-159 
0-222 
0-286 
0-352 
Xlla. Theoretical . . . 
0-0055 
0-0220 
0-0495 
0-088 
0-1375 
0-198 
0-2695 
0-352 
* The batteries were on November 29th restored to their normal current-force by the addition of 
hydrochloric acid as described in the footnote to page 112, the cells then had an electro-motive force 
of 1'052 volt ; before the addition of acid the fluid was slightly alkaline, and a cell was found to have an 
electro-motive force of 1‘024 volt, which is not much less than that of the restored cell. Consequently 
the additional length of spark XXIII., XXIV., and XXV. cannot be accounted for by a greater electro- 
motive force at the time the experiment was made. -—December 13, 1877. 
