62 Royal Society :— 
Il. Plan for rapid self-recording signals by air wires and short 
submarine cables. 
The consideration of the preceding plans has led me to think of a 
system of working air lines, and short submarine lines, by which 
great rapidity of utterance, considerably greater I believe than any 
hitherto practised, may be attained. I have no doubt but that on 
this system five or six distinct letters per second, or sixty words per 
minute, may be readily delivered through air lines and submarine 
lines up to 100 miles, or perhaps even considerably more, of length, 
and recorded by a self-acting apparatus, which I shall describe in a 
communication I hope to make to the Royal Society before its next 
meeting. 
“On Practical Methods for Rapid Signalling by the Electric Tele- 
graph.” (Second communication.) By Prof. W. Thomson, F.R.S, 
I. Further remarks on proposed method for great distances. 
Since my former communication on this subject I have worked out 
the determination of operations performed at one extremity of a sub- 
marine wire, so adjusted, that when the other extremity is kept con- 
stantly uninsulated, the subsidence of the electricity in the wire 
shall follow the triple harmonic law (that is to say, the electrical 
potential shall ultimately vary along the wire in proportion to the 
sine of the distance from either end, one-third of the length of the wire 
being taken as 180°). The condensation of' the electrical pulse at the 
receiving extremity, due to such operations, is of course considerably 
greater than that which is obtained from operations leading only to 
the double harmonic as described in my last communication ; but 
experience will be necessary to test whether or not the precision of 
adjustment in the operations required to obtain the advantages which 
the theory indicates, can be attained in practice when so high a 
degree of condensation is aimed at. The theory shows exactly what 
amount and duration of residual charge in the wire would result 
from stated deviations from perfect accuracy in the adjustments of 
the operations; but it cannot be known for certain, without actual 
trial, within what limit such deviations can be kept in practice. 
From Weber’s experiments on the electric conductivity of copper, 
and from measurements which I have made on specimens of the 
eable now in process of manufacture for the Atlantic telegraph, I 
think it highly probable that, with an alphabet of twenty letters, one 
letter could be delivered every two seconds between Newfoundland 
and Ireland (which would give, without any condensed code, six 
words per minute) on the general plan which I explained in my last 
communication ; and that no higher battery power than from 150 to 
200 small cells of Daniell’s (perhaps even considerably less) would 
be required. Whether or not this system may ultimately be found 
preferable to the very simple and undoubtedly practicable method of 
telegraphing invented by Mr. Wildman Whitehouse, can scarcely be 
decided until one or both methods shall have been tested on a cable 
