166 Trans. Acad. Sct. of St. Louis. 
water-pipe system. The other terminal was grounded 
on a gas pipe. The lead wires were clamped between 
the leaves of two small brass door-hinges, one leaf of 
each hinge being soldered to one of the ends of the rods 
at the gap. Between the gap in which the leaves were 
mounted and the ground was placed a large battery jar 
filled with four litres of a solution of common salt. The 
wire was parted at this point, and the ends were im- 
mersed in this solution which thus formed part of the 
ground cireuit. One of the wires penetrated the liquid 
to a depth of about half a cm. Between the gap in which 
the wires were mounted and the machine was a spark 
gap, between knobs of equal radius. The condenser con- 
sisted of forty large sheets of glass (36x36 inches) hav- 
ing upon them 2x40 square feet of tinfoil. The machine 
was driven by a single-phase electric motor. Below the 
lead wires a sheet of white paper was laid upon a plate 
of glass. 
It was found that there was a marked difference be- 
tween the effect of the positive and the negative dis- 
charges upon the lead wire. The resistance of the gap 
in the salt solution could be so adjusted, that the nega- 
tive discharge, or the compression wave, would cause 
the lead wire to fuse and drop in hot globules upon the 
paper below. The effect upon the paper is shown in Plate 
XLIV, Fig. 1. 
With the same adjustment, the positive discharge 
causes the lead wires to rise in a cloud of dust. If the 
paper were placed 3 em. below the wires, it would usually 
be practically unaffected when the positive discharge 
was used. In a few cases, as in Fig. 2, it was slightly dis- 
colored by the lead fumes. 
Of course the discharge could be made greater, so that 
either discharge would cause the lead to be dissipated in 
a cloud. It could be made less, so that fused metal would 
fall upon the paper when the positive terminal was con- 
nected with the ground line containing the wire. In all 
cases the cloud effect was the more marked in case of the 
