ELECTRICAL SIGNALLING AND THE SIPHON RECORDER. 365 
is kept in a state of strain by the torsion npon the platinum 
wire t , from which the siphon depends. When the coil is de- 
flected so as to increase the tension on the fibre, /, the top 
of the siphon is pulled nearer to the coil, and the writing 
extremity moves across the paper pp further from the coil ; 
and when the coil is deflected so as to decrease the tension, the 
motions of the siphon are the reverse. 
The two electro-magnets, which have each a pole m m 
shown upon the figure, are simply rods of soft iron wrapped 
round with copper wire, which is insulated by a covering of 
spun silk. So long as a current of electricity is sent through 
this wire the iron core about which it is wound becomes a 
magnet, but so soon as the current ceases to flow the mag- 
netism vanishes almost entirely if the iron be very soft. The 
amount of deflection of the coil is proportional to the strength 
of the electro-magnetism, to the length of wire in the move- 
able coil, and to the strength of the current which flows through 
it ; so that, cceteris paribus , the stronger the current upon the 
electro-magnets the greater the range of the siphon point 
across the paper. There is, however, a certain convenient range 
which can always be procured by regulating- the battery power 
upon the electro-magnet and the current which comes from the 
cable. In the instrument itself every contingency in the work- 
ing is provided for, and there are adjustments to regulate its 
every part, but the description of these would be uninteresting 
to many. 
Suppose now that it is desired to transmit a message along 
the submarine cable from Falmouth to Lisbon. The source of 
the electricity to be employed is, we shall say, the ordinary 
Daniell battery, each element of which consists of zinc immersed 
in a solution of sulphate of zinc and a plate of copper immersed 
in a solution of sulphate of copper, the two solutions being kept 
separate by a porous separator. All the elements are joined 
up 44 in series,” that is, taking them in order the zinc plate of 
each is connected to the copper plate of the next. If the 
last copper plate be joined outside the battery by any conduct- 
ing circuit to the first zinc plate, a current will flow from it to 
the zinc. This conducting circuit may be a very complicated 
one, but still the current will find its way along it, always from 
the Copper plate to the zinc, even although its route may take 
it round the world. In submarine telegraphy this conducting 
circuit is formed by the cable, the receiving apparatus, and the 
earth itself. If the zinc plate of a battery at any station, as 
Falmouth in England, h well connected to the earth — by one 
of the city water-pipes, for instance— or a large metal 
plate buried deeply in the ground, and an insulated wire be 
led from the copper plate to a distant station, such as Lisbon, 
