ELECTRIC DISCHARGE WITH THE CHLORIDE OF SILVER BATTERY. 
79 
ratio of the square root of the odd numbers 1, 3, 5, &c., the sectional areas being 
consequently in the ratio of the odd numbers. The first ordinate was taken as 1’33 
to the first abscissa 1. A diagram was laid down with 120 such ordinates to a 
scale of four feet for the length of the point, and then reduced by successive 
steps with a pantagraph to the size shown in fig. 13, X, this, with a certain modifi- 
cation,* served as a guide for a cutting-pantagraph to shape a cutting tool to be 
used in a lathe for forming the point of the size Y, fig. 13, to be actually used as 
Fig. 13. Fig. 14. 
a terminal. Experiment proved that all the points made with this tool gave 
the mean length of spark obtained previously, namely, with 8040 cells, 0‘340-0'350 
inch. 
The greater part of the curve of the point so laid down corresponds to a para- 
boloid or more correctly to intersecting parabolas. 
We were induced to construct a second tool to make a truly paraboloidal point such 
as is shown in fig. 14 at X' and Y' ; this new point gave precisely the same length 
of spark, although it will be seen that the extremity of it (X') does not terminate 
in an actual point like in fig. X. Subjoined are the lengths of spark between a point 
positive and a disc negative, which we quote to show the constancy of the results 
under the same conditions. 
* As the guiding arm of the pantagraph carries a point which works in a groove, whilst the cutter 
to form the tool is a cylinder, a guide line parallel to the curve of X, but distant four times the radius of 
the cutter, has to be laid down to guide the tracing point, the reduction being to one-fourth. 
