oy i 
78 Velocity of the Galvanic Current in Telegraph Wires. 
* fidence—that the velocity of the electrotome and electropea sig- 
nals is the same. The latter is, however, inversely proportional 
to the sum of all the induction-times of the molecules on the 
line of wire,—the former to the sum of their eduction-times. 
If these are equal for the wire, the inference is natural that they 
are equal for the iron enclosed in the helix, if this be as soft as 
the iron of the w 
Such apactlatigne are indeed loose, and would not be warrant- 
the question. But, as the problem now presents itself to us, eve- 
“rything appears interesting and hae consideration, which 
affords opportunity even for a presumptio 
In the apparatus used by my friend Prof ‘Mitchel, he considers* 
that he is able actually to measure the length of the armature 
time, which is the sum of the induction and pass-times. The 
method which he uses is, however, ee of being applied to 
the record made with Morse’s insttum 
In an earlier part of my remarks, L deferred the discussion of 
the question whether the electrotomes and electropaeas traveled 
with the same velocity, and yet have just now expressed the 
opinion that they did. The opinion was formed as follows: 
We have the length of the recorded elock- -pause, C=c—e4? 
+p, and of the recorded signal-pause, S=s ~e+7+p. 
_If we take the difference of these, the three unknown quanti- 
ties disappear, and we have C -S=c—s, the difference of the 
real duration of the pauses, equal the difference of their recorded 
duration. The only assumption here made is that the induction, 
eduction and pass-times are the same for both pauses,—an as- 
sumption quite warrantable if we compare each signal-pause with 
the clock-pause nearest it. 'They will then rarely be more than 
a quarter of a second distant from one another, and the valuesof 
the corrections are not likely to change appreciably within so 
short an interval. I have formed a table of the differenees i in the 
length of the same signal and clock-dots, for six different tele- 
graph-stations on the “line between Washington and St. Louis, 
and, from the discussion of more than a hundred different signals, 
ae 
find that the mean of these differences is almost identical for all 
the stations. 
The intensity of the current even at the same place is quite 
Say unequal, owing to various influences, among which are thermo- 
metric and hygrometric changes in the atmosphere, which affect 
: fhe Jealation and the conduction; want of constancy in the bat- 
hose activity varies very much with variations of tem- 
ive: want of homogeneity in the substance of the plates; 
pera 
the the continual formationt and flaking off of coatings of vox al and 
® a 16. + Faraday, Researches, 
