MR. GROVE ON THE ELECTRO-CHEMICAL POLARITY OF GASES. 
99 
Postscript, April 24th. 
I may, I trust, be permitted to add to this paper one or two experiments on the 
subject last discussed. Assuming that the alternations of oxidation and reduction 
were produced by interference in consequence of the discharge proceeding from suc- 
cessive points of the terminal or terminals, a difference of effect might be anticipated 
if the electricity passed from a point only, and not from a line as was the case in Ex- 
periment 13. I therefore sealed a platinum wire ^th of an inch in diameter into a 
piece of glass tubing, and then ground the extremity to a flat surface, so that the 
section only of the wire was exposed ; this wire was placed opposite, and at 0 07 of 
an inch distance from the polished silver plate, in a mixture of one volume of oxygen 
with five volumes of hydrogen attenuated until the barometer stood at half an inch ; 
discharges from the secondary coil were then passed, the plate being positive, and a 
round dark spot of oxide formed represented at fig. 8 ; the platinum sealed in glass 
was then removed and the steel needle substituted for it, all else, viz. plate, gas, 
barometer height, &c., being the same : the system of rings represented at fig. 9 
was now produced. 
Another experiment was made, directed to the same point : a wire of copper 0‘04 
inch diameter, and a thread of glass of the same diameter were attached by sealing- 
wax at their extremities in a horizontal position 0’025 of an inch from different parts 
of a silver plate, being insulated from the silver by the wax interposed at the extre- 
mities. The gaseous mixture and barometric height being the same as in the last 
experiment, and the silver plate made positive, when the platinum wire sealed in 
glass was brought near the plate, and the discharges passed, a spot similar to fig. 8 was 
formed ; but when the coated point of platinum was brought over the copper wire at 
0'02 inch distance, a figure consisting of two separated semicircles was formed, 
having spots in the bisection of the chords, as shown at fig. 10, the portion between 
the spots and the semicircular line of oxide being of polished silver. With the glass 
thread the effect was the same, but produced with greater difficulty and not so well 
defined. 
In many repetitions of these experiments which I have made, I have invariably 
produced the alternately polished and oxidated rings from the bare wire, and have 
not procured them from the coated wire, except to a very slight degree, and under 
certain circumstances, which, as far as I could trace, were as follows : — 
1st. When the extremity of the wire was very near the plate, so that it had a 
sensible magnitude with reference to the intervening space, a slight formation of 
minute rings could be detected at the commencement of the experiment. 
2nd. When the experiment was long continued, or when the coated platinum wire 
had been used for previous experiments, a set of rings, not consisting of an alterna- 
tion of oxidated and polished rings, but of annuli of different degrees of oxidation, 
were formed. 
o 2 
