28 SEVENTH REPORT—1837. 
soon as the surfaces of contact are of such magnitude that decompo- 
sition is no longer effected, the thermometer reaches a maximum, 
which it does not pass, even when the surfaces of contact are aug- — 
mented. This fact seems to prove, that chemical decomposition pro- 
duced by electrical currents takes place only when these currents 
undergo a certain resistance in their passage from the metal into the 
liquid ; and that, when this resistance does not exist, decomposition 
ceases. When we employ wires of platina to transmit the magneto- 
electric currents into a solution of any kind, whether acid, saline, 
or alkaline, we, at first, observe an abundant evolution of gas; then — 
this disengagement diminishes, and at the end of fifteen or twenty 
minutes it altogether disappears. When we examine these metallic 
wires, we find them covered with a very fine powder, composed of 
platina in the metallic state, but extremely divided. The same phe- 
nomenon takes place with gold, palladium, silver, &c. All these 
metals are covered, in the same manner, with a very fine coating of ~ 
the metal itself, in a state of extreme subdivision. The author has 
assured himself that this powder is composed of the metal itself, and 
not an oxide or a suboxide. He inquired whether this effect is the 
result of the mechanical shocks that the molecules of the metal undergo 
by the action of these currents, which are discontinuous, and alter- 
nately in opposite directions ; and whether it would not be augmented 
by the succession of oxidations and deoxidations, which would occur 
on the surface of the wires. He concluded by stating, that he had 
observed that the armatures of soft iron, (about which the metallic 
wires are coiled, in which the currents are developed by induction,) 
cease to be attracted by the poles of the magnets, before which they 
pass when the two ends of the wire in which the current is developed 
are united by one good metallic conductor ; a fact which would seem 
to prove that Magnetism and Dynamical Electricity are, in these 
cases, but two different forms of the same force, one of which dis- 
appears when the other becomes apparent; and he insisted on the 
advantage that we might derive from this property in the production 
of motion by electro-magnets. 
On the two Electricities, and on Professor Wheatstone’s Determination 
of the Velocity of Electric Light. By W. Errricx. 
On the occurrence of the Aurora Borealis in England during summer ; 
with a recommendation that the phenomenon should, at all seasons, be 
more carefully observed than hitherto. By 8. Hunter Curistig, 
M.A., Sec. R.S., §c. 
The occurrence of an Aurora borealis in the very middle of summer } 
is a phenomenon hitherto unrecorded, and as no account, that Iam — 
aware of, has appeared of avery brilliant Aurora which was exhibited 
eb heer.” 
