ELECTRIC COLUMN, 
S13 
fartlier proof that they contain it. They ere both ot" wch a 
nature, that they are decopjposed wlven too much <;u>mpreibed, 
in which case some of their ingredients are inaiiifeslcJ. 
We have again on this object todirectus, the anaU>gy between An»loi;ic:il 
steam, fire, and the electric fluid j for as the whple of the com- 
position of steam is known, it illustrates the correspondent 
phenomena of the two other fluids. Steam is compo»ed of fire 
and water in an elastic form; and when it is com|iressed in a 
metallic barrel, as, for instance, in that of the air guu, in which 
the air compressed is always mixed with aqueous vapour, which 
the strong compression decomposes, the fire diseugagtd heats 
the barrel, and the water is collected on its sides and at the 
bottom. 
Here we see the whole process, which explains, by analogy, 
the known phenomenon, that w'hcn a bar of iron is hammered, 
and thus the fiie contained in its pores is compressed, its heat js 
increased, till at last it glows, by ^ho decouxpo-dtion of seme of 
the particles of fire. This is the rcitson why the same bar, 
when it luTs cooled, cannot bo made again to glow by hanuuGi- 
ing ; because it cannot be farther compressed : and fro<n tome 
effect produced by a new' combioation of the matter ol fiie with 
the iron, this becomes brittle. 
Thus also, when the eJ«ctric fluid becomes sod-Ji^ as lo Coctricity^ 
^patk, a part of it being decomposed, light is emiued ; and I 
•liave proved directly, by an experiment related in p..42'3,pf th« 
list vol. of my work, 1 dees Sur la.Meteorologic, that when the 
;ffectric fluid emits sparl\^, Its quantity is diininbbed. For this 
;ixperimeot, I used two large jusplated brass disks, having com- 
parable electrometers : the disks were so disposed as to .front 
;;ach other at a small distance. 1-madc one of these disks to 
immmunicate with the rubber of .an electric machine, aod the 
Dolher with a small prime conductor, by which means, one of 
: he disks became positive,, at the expense of the otlier, renderevi 
negative to the same degiee, as shewn by the eleoUooieters, 
t.nd in thatstato I .separated the disks tVom the el«actric m^hine. 
Each of the disks. Ivtd a moveahle boll ; aad these baijii.were-Tt.f o.'iper;- 
t'.ept, hy springs, at a certain distaace from each ptbpr, whilts“^“' 
thtf 
