52 REPORT—1848. 
bination and volume are found to hold universally. On these principles Mr. Exley 
calculates the specific gravity of gaseous bodies by multiplying the atomic weight, on 
the hydrogen scale, by 10, and dividing by 144, when the volume is contracted one 
half; and again, by 2, when the volume is unaltered; thus, for ether the atomic 
weight is 74, then 740-12 X 12 X 2=2°5694. Gay-Lussac finds it 2°586 by ex- 
periment. Thus are these laws established. : 
Since it is shown by the theory, and proved by experiment, that equal gaseous 
volumes of hydrogen H, nitrogen N, nitrous acid O.N, olefiant gas H,C, etherine 
H,C., cetine H),Cs, &c., contain an equal number of atoms, the centres or centres 
of gravity of the atoms, simple or compound, are equidistant, and that distance is 
not altered when every two are united by intervenient electric atoms, or by such 
atoms and any number of elementary atoms whatever, if they are screened by the elec- 
tric atoms, so as not to become centres of support. 
On the Motion of the Electric Fluid along Conductors. 
By the Rev. Tuomas Extey, M.A. 
Professor Wheatstone made some valuable experiments, showing that in traversing 
a long conductor the electric spark occurs at the same time at each end of the circuit, 
and latest at some part near the middle; this has been considered as a proof that 
there are two electric fluids; but this conclusion is too hasty, for it may be shown 
that the phenomena ought to be such on the supposition of a single fluid. 
When an electrical charged plate is discharged, there are only three ways, worthy 
of notice, by which the equilibrium can be restored :— 
1. The passage of the fluid through the circuit, commencing either at the posi- 
tive or negative end. 
2. Its passage in pulses beginning at one or the other end. 
3. Its passage in pulses taking their rise simultaneously at both ends and closing 
about the middle. 
In order to obtain correct views we must attend to the phenomena of charging 
an electric plate. 
If the knob of the prime conductor, electrified to a certain intensity, were pre- 
sented to the bare surface of a thin plate of glass, the particles of the glass would 
receive and retain a small quantity of the electric fluid without suffering it to pass on 
far, or they would give a small quantity without receiving a fresh supply from distant 
particles; a higher intensity or a nearer approach of the prime conductor would give 
or take another spark, and the neighbouring particles of the glass would receive or 
give fluid to a small distance farther, where the progress would be arrested. 
But when the plate is furnished with the usual coating, the spark of electric fluid 
affects in like manner all the superficial particles of the glass to the limits of the 
coating. If now an uninsulated conductor be presented to the opposite side, a spark 
will pass between it and the coating, and at the same time another spark between 
the prime conductor and the coating, and a succession of simultaneous sparks on the 
opposite sides will occur so long as the same intensity of the conductor is maintained, 
until the plate is charged. 
These phenomena assure us, that although the fluid penetrates only to a very 
small depth in the glass plate, yet the addition-or abstraction of the fluid affects the 
particles of the plate, as far as the opposite side, producing in them a tendency to 
give fluid to, or to receive fluid from, the uninsulated conductor on the other side. 
Thus the particles of the glass have obtained a tendency to receive fluid on the sides 
towards the positive conductor and to give it from their opposite sides, Thus will 
all the particles of the glass which are situated directly between the opposite con- 
ductors be affected; but at a distance from that line of particles, both sides of the 
plate will be in the same condition as the prime conductor by which the charge is 
made. When the charged plate is removed, the receiving sides of the particles will 
be towards the negative surface of the plate, and the delivering sides towards the 
positive surface. The discharging rod being now applied with its knobs at such a 
distance as not to receive a spark, the same condition of the particles will remain in 
the plate, and will be propagated in the same direction on the particles of air conti- 
guous to the rod through the whole circuit; the particles of air contiguous to the 
