ON PRINTING TELEGRAPHS. 
297 
By means of a series of sucli relays, direct communication is 
effected between London, Berlin, and St. Petersburg, or even 
more distant cities. 
We have described the Morse apparatus in its simplest 
form, for the limits of our paper do not permit enlarging upon 
the contrivances for neutralizing the effects of induction in 
submarine cables, for cutting off the leakage from neigh- 
bouring wires, and for increasing the sensibility of the appa- 
ratus. It is, however, necessary to mention one point. As 
it is not possible to transmit to a great distance a current 
sufficiently strong to produce a powerful mechanical action, 
the current received from the sending* station is made to act 
on a relay connected with as powerful a battery as may be 
required to set in motion the Morse apparatus. 
The speed attained by the Morse system varies with the 
nature of the despatch. Intelligence or news can be worked 
off much faster than private messages. A first-rate clerk has 
been known to send between sixty and seventy Stock Exchange 
messages per hour, but thirty to thirty-four words per minute is 
excellent work, the receiver, of course, writing for himself. 
Owing to the facility afforded by the system of transmission 
by relay, or as it is called, translation, despatches can be sent 
to stations, on separate and distinct wires, at the same time 
by a single clerk. The debates in Parliament, Re uteris tele- 
grams, and the other items of telegraphic news which appear 
in the country papers, are now frequently manifolded in this 
manner — to six, seven, or even more stations at the same time, 
and it would be quite possible, if it were desirable to do it, 
that a single clerk in London should supply every large town 
in the kingdom, at one and the same moment. 
The printing telegraph first used here, and still partially 
employed, is, however, not that of Professor Morse, but an 
invention of Bain, of Edinburgh, founded on the chemical effects 
of electricity. When a current is caused to pass through the solu- 
tion of a chemical compound, it decomposes it, or separates its 
component parts, in many cases producing an alteration in 
colour, either by causing the wire which conveys the current to 
be dissolved, or by separating a coloured solid substance from a 
solution previously colourless. Thus if a current be made to 
pass through paper soaked in iodide of potassium, iodine, a 
solid substance, will be separated at the wire connected to the 
copper of the battery, and a brown stain will be produced. 
Soak a sheet of printing-paper in a mixture of equal parts of 
saturated solutions of the ferrocyanide of potassium and nitrate 
of ammonia, diluted with an equal volume of water ; blot it off 
and lay it smoothly on a plate of zinc or sheet of tinfoil, con- 
nected with the ?inc of a Daniell battery of twenty cells. By 
