1879.] 071 Midhple Telegraphy. 199 



There is another disturbance besides that prodiieed by rain or 

 weather, and that is one due to the existence in a telegrai^hic line of 

 what is called electrostatic induction. This is a very hard word, but 

 it really means something similar to the effect of friction in pij^cs on 

 the flow of water or gas. When gas or water is forced through pipes, 

 a (j[uantity of it adheres to the sides, and produces a diminution of 

 pressure due to friction. So, when we try to force electricity through 

 a wire, a quantity of it adheres, as it were, to the sides of the wire, 

 remains there as a charge, and diminishes the action of the current, 

 and produces what is called retardation in signals. Eetardation 

 means really reducing the rate at which we work. If it is possible, 

 say, between London and Aberdeen to work as fast as ever we like, 

 then if we attempt to work over a submarine cable of equal length the 

 speed diminishes very greatly indeed. Between London and Cork, and 

 between London and Aberdeen we are at the present moment working 

 practically as fast as the instruments will run, at the rate of about 

 150 words a minute, while through the Atlantic cable, with all their 

 skill, they cannot work at more than twenty-five words a minute, and 

 this is due to the disturbing element of electrostatic induction. To 

 compensate for this it is necessary to make your artificial line exactly 

 similar in all respects to your real line, and, with duplex circuits, this 

 is done by inserting, in addition to the rheostat, a condenser. A 

 condenser is simply a series of leaves of tinfoil separated by paraffined 

 paper. A series of alternate paraffined papers and tinfoil really 

 comprise a Leyden jar, and such a Ley den jar w^ould have the capacity 

 of retaining a charge similar to that retained by the line ; and it is 

 only necessary to increase the size of the condenser until the same 

 electrostatic capacity in it is obtained as is experienced in the line 

 itself. Here is a condenser which has not the appearance of being a 

 very formidable instrument, but it has sufficient electrostatic capacity 

 to compensate for a line about 200 miles long. 



"We will now work the quadruplex a2:»paratus before you. I do 

 not hope to have made you comprehend the action of the system ; I 

 only hope that I have given you an idea whicl: you can work out for 

 yourselves, and which will give you more interest in seeing the system 

 in actual operation. 



(Communication was then opened with the Central Telegraph 

 Station, and several messages were sent to and from the Institution 

 on the quadruplex apparatus.) 



Many peoj)le are suspicious of operations of this kind going on at 

 lectures. I may tell you that a few years ago I gave a lecture at 

 Southampton, and took special care to have a wire joined through 

 London to the Continent (we only had one cable at that time), and at 

 the proper period of the evening spoke to London, Vienna, Berlin, 

 and Amsterdam, and received answers. I then asked what time it 

 was in Vienna (it was nine o'clock in Southampton), and received 

 answer, "Twenty minutes past eight." This was wrong, and it 

 turned out that a clerk in London had been personating the 



