Sacramento daily record-union. [volume] (Sacramento [Calif.]) 1875-1891, 1882-09-16
ELECTRICAL RESISTANCE.

By electrical resistance is meant the op-
position offered By every constituent part
Of the circuit to the passage of a current.
There is first the resistance of the genera
ting battery itself In a chemical battery
the calculated water, or electfolytc. otisfa
very high resistance then come the 70,
sistance OF the leading wires, and ia al
ditioR the resistance OF every constituent
portion of the circuit, be it electric ma
chine, resistance coil, electromagnetic,
telegraph machine, or the catbons
OF a series of electric lights; in fact,
any retardation of the current, caused
by material impeachment or by work TO
De performed, is known by the name OF re.
sistanee, which can be tested and meas.
ured but whatever obstacles current
may have TO encounter, its way must be
continuous and unbroken by the smallest
interval. It will be seen from this that re,
sistance is merely relative term. Every
substance can be electrified, some with
greater and some with less difficulty. The
metals, for instance, such as German silver
and copper, can be electrified almost IN.
simultaneously. Other substances
carbon, shellac, and putta percha-take a
very long time, and require persistent cleo.
trio exclIation TO become so. Generally
speaking, substances which can be very
easily electrified are known as conduc-
tors, and those which are slowly elec.
trified are called insulators. Neither
term is strictly accurate. It is only
question of degree. Even the best
conductor offers a certain amount of
retardatiou, aud the worst conductor known
lie permeable IN time, and does not afford
perfect insulation. To be sure, the limits
of variation in this respect are wide enough.
An uncovered wire of copper will allow
current to move along at she rate of 2SS,-
600 miles second, and it would take min.
utes, and perhaps hours, to creep over an
inch or two of gutta percha, Still, az
mathematical fact, neither insuiators nor
conductors are perfect. The two prop
critics are reciprocsls. Ii we take leo as
the standard of eonductivity or absolute
non-resistance, pure copper wire would
show, perhaps, &c or 9S of conductivity
and or 2 Of resistance. Gutta perCha,
at the other end of the scale, might show
less than / of conductivity and more than
SO Of resistance. / have not at hand the
exact figures, but these Will serve as an
illustration of the meaning. The mathe-
NAUTICAL formula known as Oam's funda.
mental law states electrical resistance
to be inversely proportional to the
strength Of the current. An illustration Of
this is seen in the case of lightning con-
ductor. A small copper wire will carry
away moderate current without disturb
ance, because the current and the resist
ance OF the wire have some manageable re-
lation to each other. But, if q fash of
Lightning were to pass along the same wire,
1t would fuse the wire because, although
the resistance would be the same, the
proportion borne by the elec,ro-motive
force Of the lightning TO the conduotivity
OF the wire, woUld have no mans geable re-
lation to the current. One the same prin-
ci2le piece of carbon introduced into q
circuit stops the passage OF feeble current,
being a bad conductor. 1t, however,
allows strong current to pass but, before
doing so, it offers such vigorous resistance
that the energy necessary to overcome the
resistance is sufficient to heat the carbon
white hot, or, if there be break in the
carbon, to cause an electric arc at the point
OF fracture. This is the principle of the
electric light.