THE SCIENCE OF THEEHBIIN
                                 PART III.H                       ]XHBIIOT
                                 PART iii.               ~~~~the wires and
the index.-needle beyond them.It will be
THE Processes of the electrotype very, naturally conducts to evident, upon
considering the construction, that by such an
   the ~onsideration of that section of the Exhibition1 within arrangement,
the index-needle must come to rest almost
which are exhibited an application of a still higher order of immediatelyatri
has been moved. Another method for
science.  Electricity-that singularl] subtile and diffusive moving they infdtex
Its to attract or repel the support placed
power, which is perhaps, of all the physical agents, the most upon its axis
by means of an electro~magnet. When we coil
active in nature-is now chained and made to do the bidding around a piece
of soft iron a quantity, of copper wire covered
Of its subduer. The marvel of modern experimental science with silk, and
connect the ends of those wires with a voltaic
is, beyond all question, the Electric Telegraph, by which we battery, the
iron becomes powerfully magnetic. The moment
are enabled to convey instantaneously our thoughts to the contact is brok-en
the magnetism is destroyed; or, by reversing
most distant point. The flight of Ariel is slow compared with the direction
of the current, the poles of the magnet are
the speed of this physical agent, which (the mechanical clif- rapidly changed.
Thus any series of attractive or repulsive
ficulties of placing the wires 'below the reach of the action of influences
can be obtained with much facility.  Brett and
breakers, when crossing seas, being overcome,) would enable Little's patent
electric te'legraph is of this order. The magnet
us to convey our desires round. the world in an instant of is in the form
of a ring or horse-shoe, and is' suspended in the
time. Those who are unacquainted with the jpeculiarities of centre of the
helices of copper wire, which are double, and of
arrangement which lead to the effective product ion of this a circular form.
This magnet is deflected either to the right
result will do well to study the instruments in the Exhibition hand or to
the left, according to the direction of the current.
of Industry by means of which telegraphic communication is The indicators
are not magnets, but are moved by the agency
now effected. It may not be regarded by our readers as out of the magnets,
b y which a distinct and certain indication is
of place if we endeavour to render the mode by which elec- insured. In the
electric printing telegraphs, similar means
tricity is generated and employed familiar.  The relation are employed to
effect the desired end of printing the intel-
between voltaic currents and magnetism must be understood. ligence communicated.
 In some, inked types are actually
it is, therefore, necessary that this should be clearly but employed, and
brought into contact with the paper by the
succinctly described., Voltaic currents are generated by che- force of an
electro-magnet. In others, whenever connection
mical action. A~n acid, usually sulphuric, is made to act upon is made, the
electricity effects chemical decomposition. When
zinc plates, which are placed in juxtaposition with, and con- it is interrupted,
no change takes place. Thus any number
nected by, a wire to a copper plate. The electric action is or variety of
marks can be impressed at any distance from the
dependent on the different chemical affinity of the liquid for communicator
with great rapidity.  The chemical agents
the respective metals: it will dissolve the zinc, but not the usually employed
to produce the marks on the paper are the
copper. Water is decomposed during the action. Hydro en ferro-cyanide of
potassium, which, being decomposed, gives
makes its escape at the surface of the copper plate, and the rise to the
prussiate of iron,anmkeadepbuiprso;
oxygen& combines with the zinc to form oxide of zinc. The or the iodide
of potassium and starch, which is white,-but
law of action as established by the researches of Faraday is, by the battery
action, iodide of starch, a very dark purple
that the quantity of electricity liberated is exactly equal to substance,
is produced, so that the letters or signs are
that which was necessary to hold together in their original impressed in
a dark colour. All that is here attempted is to
states the substances undergoing chemical change.  During give an outline
of the processes adopted ; with the modifications
this disturbance of the electrical equilibrium, a portion passes of these,
and the details which are introduced for the purpose
through the liquid to the copper plate, and back through the of facilitating
communication, space prevents our dealing.
connecting band to the zinc plate. Howsoever great may be   Bakewell's Electric
Telegraph possesses the peculiarity of
the length of the connecting wires between the plates, the transmittingfac-Similes
of the hand-writing of correspondents,
disturbance is communicated along the whole length of the so that their signatures
can be identified. This is so in-
line.  The difference between the result, when the dis. geniously effected,
that we must endeavour to render the
tance is but a few inches, and when it is extended over arrangements adopted
intelligible.  The transmitting and
many miles, is only lessened by the degree of resistance receiving instruments
are of the same description. Trains of
offered by the metallic wires to the propagation or onward wheels moved by
weights impart uniform motion to each;
movement of the disturbance. We speak of a current tra.- these are allowed
to act, or are checked, by the action of
versing the wires. Our language, here imperfectly applied, is electro-magnets,
in Connection with a voltaic battery. As the
often v~ery incorrectly understood; an idea of something flowing power is
derived from. the same source, the machinery, at
is usually conveyed to the mind by this form of expression. This, whatever
distance the two arrangements may be frmec
is not the case,- motion is communicated to one point of other, is equally
affected; the movement of the wheels and
the mass, which is transmitted    to the other, or rather is weights being
isochronous. On each instrument is a metal
sensible at that extremity.   At the time of this electrical cylinder, and
over each cylinder mbetal styles, which press
progression, the wire is magnetic,-that is, it will attract iron lightly
oney  scnncedwt the cylinders frmed oed.Oeo   thepoe
in the same manner as a magnet does. If we hang up a of the vlacbteyi   
        once      ihteclneso         h
magnetic piece of iron, so that it swings parallel to, and over intrmnt,
n               the ohrwttesyl.Tu satho etw
     or uder he wrethis iron is unmoved it an. electric disturb- systems
of arrangement are always in preciselytesm
ance is not circulating ; but the moment that the force moves, electrical
Conditinthsbngceryudsodhef-
from    connexion being made with a battery in action, the iron lowing mode
of electro-printing, or writing, will be intelligible.
is swung round at right angles to the direction of the wire. The messageto
besndsrte on atheetra  ofmitin-foilwither
When contact is broken, and no electricity is traversing, it sealing-wax
varnish, this is placedo th  e transmi kttin  cylnder
returns to the line of the wire; connection being made, it is all the lines
covered by the varnish serve obektecn
           againdefleted.  avin  a poer ofthusmoig a magnetic nection. On
the receiving cylinder a sheet of paper moistened
needle at any distance from the battery, we obtain the means with acidul
ted   , feetro-pusaeocoahemisa deoplacetwhnthe
of giving signals and of conveying signs.  For the purpose of connection
is complentedreuetrono-chicarsdecmosting  iaks
      inceasng hiseffctthe wire is bent many times around a effected, and
where any intrrupiong occur inchange ti-olakes
      magneic nedleso that the  current passing  frequently place.  Now the
cylnecarigtensibdi-flad
along the length of the helix produces an increased effetIntaonwihsplcdherprdpprmvgatheae
thi's manner the weakest disturbances are rendered sensible. rates, the current
is interrupted by the varnishwiigi
              Uponthi prncile he  eedl teegrphsarecontruted. both at the
same time.  All the parts of the paper on which
                    Thesneelearang mentare ofsverl ki ds; he  geat   he m
tal tyl sprs, when  theyare in.connectionwiththe
object being to obtain rapidity of deflection and freedom from  'ntin-foilbemebuall
those. Hecorespnigwt the  varnis
oscillation.  The comp ound needle is that which is mot  ore-o  whthverfoitrmainhie.
oenc thhe witnglsgn, rawing,
quently employed, and it consists of a  very thin ivory disc,  rwaee  tmybo
     the tin- fomilsareofa ithulree-
             whic sutais seera hihly  ugntisd shrt eedesfirmly sente on the
prepared paper, hundreds fmlsfo  t
       Secredto t.  hiscomoun aragngeenti ipaed  bhrtn etween  The application
 of the subtile power of electricity to
              whichsustans seeral ighly  is paced  etwee