Velocity of the Galvanic Current in Telegraph Wires. 79 
many other circumstances. We have already seen that the pass- 
time varies with the intensity of the electro-magnetism in the 
iron and consequently* with the intensity of the current,—and 
can therefore infer that the different clock pauses would not ap- 
pear of the same length even on the same registers. That they 
do not, may be inferred from the following table, which gives 
_the mean value of clock-pauses at each station for each one o 
} five successive minutes. 
MEAN LENGTH OF CLOCK-PAUSE. 
,. 8.8. p PRES GS C.,. ae ae St. 
. 8h.47 Os072 | 0068 0:055 0095 | 0-096 o-oo" 
48 0-091 0-050 0-067 0-090 | 0-093 0°100 
49 0-094 0-065 0055 0-084 | 0125 0110 
50 0:103 0-071 0:059 0-081 0103 0-118 
51 0-100 0-078 0-055 0081 | 0098 | 0102 _ 
Mean. 0-091 0-067 0-058 0087 | O104 | 0109 
to irregularities and im 
Tegistering apparatus. 
Bain’s galvano-chemical telegraph affords an opportunity of 
trying the experiment under circumstances totally independent 
of the pass-time, which has proved so troublesome in the experi- 
ments made with Morse’s apparatus. The paper on which the 
tecord of Bain’s telegraph is made, is colored with a solution of 
ferrocyanate of potash. It rests upon a revolving metallic disc 
connected with one pole of the battery, while a needle or finely 
pointed wire connected with the other pole, trails on the peer 
Surface. When the circuit is closed, the current passes between 
the needle and the metallic disc, coloring the paper in its passage 
is by the partial decomposition of the ferrocyanate. Walker has 
perfections in the mechanical part of the 
SR etme 
ie Fechner, Schw. n. Jahrb., ix, pp. 274, 816. Lenz and Jacobi, Pogg. Annalen, 
233, Bull. de l'Acad. de Pétersburg, vol. iv. 
, 272. 
sate 
