OF ELECTEIC SIGNALS THEOEGH SUBMARINE CABLES. 
997 
A strip of paper (figs. 8 & 9, Plate L.) was prepared with two parallel rows of alternate 
holes. This paper was joined so as to form an endless band, and was drawn by the roller 
E imder two little bent wires h and e, placed abreast, so that each alternately came in 
contact with the metal plate L through one of the holes in the paper. The plate L 
was connected with the cable, the wire h with the battery, and the wire e with earth. 
As the paper was drawn along under the wires, the alternate battery and earth contacts 
sent signals through the cable, and the length of the holes in the paper determined the 
relative length of the contacts. 
The first or battery-contact was made through the upper row of holes (fig. 9), the 
earth-contact through the lower row. Dots were sent by two equal holes, dashes by 
two longer holes, of which the upper bore to the lower the proportion of 6 to 4, corre- 
sponding to the relative length of contacts desired. The length of the two dash con- 
tacts was made equal to two pairs of dot contacts. 
It was expected that if the right proportion between the first and second dash 
contacts had been adopted, all confusion from irregular combinations would be avoided ; 
but during any pause, such as is practically required to separate groups of signals, the 
spot or current would still fall towards zero if the line were left in contact with the 
earth (or even if insulated at one end), so that the first signals sent after a pause would 
still cause mere irregular and unintelligible changes in the received current. To avoid 
this second source of confusion, it was necessary to maintain the received current, during 
any pause, at the constant final strength to which it returned at the end of each oscil- 
lation during a series of signals. 
If this were done, the first signal would begin where the last left oif, and each signal 
might be expected in all cases to produce one invariable and intelligible effect. 
There were two obvious means of keeping up the current during a pause. The line 
might be left in contact with a third source of electricity* just sufficiently powerful to 
maintain the required strength of current, or a very rapid series of contacts might be 
made alternately with the full battery and with earth. Experiment had shown that 
such a series of contacts would maintain the current at the receiving end sensibly con- 
stant, and the strength of this constant current could be easily adjusted by varying the 
proportion between the first and second of these very short contacts, increasing the 
length of the first contact to raise the current, and increasing the length of the second 
contact to lower the current. 
This second plan was easily carried out by the perforated paper. Where a pause was 
• "WTien reverse currents are used, if the line is put in contact with earth during a pause, the confusion 
of the first signals will be much lessened ; the earth then acts as the third intermediate source of electricity 
alluded to in the text. This plan has to some extent been adopted in practice by Messrs. Siemens and 
Halske, by means of a key invented by Mr. L. Loeeelee. This benefit, which may perhaps account for 
the fancied superiority of reverse currents, might be equally obtained with simple currents by connecting 
the line during each pause with half the battery. Mr. C. F. Vaelet informed the author that he also has 
used a similar key for a considerable time. 
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