Velocity of the Galvanic Current in Telegraph Wires. 71 
a reply. 
In the electro-magnetic telegraph offices, using Morse’s ] ie 
signals are communicated by the magnetization of a piece of soft 
jron, in the form of a horse-shoe magnet, and placed within a 
helix of wire. When the current flows, the iron becomes mag- 
netic, and attracts an armature placed before it and connected 
with a graving tool. An endless fillet of paper is kept moving 
beneath the graver, by means of clock-work, so that the fillet is. 
unmarked when no current exists in the wire, but is grooved by” 
| the action of the tool while the circuit is closed. - 
_ Fig. 1, (see Plate, ) represents the recording apparatus and its ad- 
justments. M is the magnet, A the armature, which is held back by 
the spiral spring S, while the current is not flowing, but is attracted 
as soon as the circulation of the current through the helix of wire 
experiments between Washington and St. Louis ought to furnish 
me 
~*~ 
upon the roller R?. The roller R? receives motion from the 
wheelwork W, and communicates it to the paper fillet F. While 
the armature is attracted, the indentor at the end of lever L 
te 
¥ 
a: 
us 
ca % 
capable of adjustment by screws. ‘The distance traversed by the 
armature in passing from the outer to the inner stop is technically 
called the pass. 
As the wire may be coiled into any number of helixes in the. 
course of a circuit, there is no practical limit to the number of 
intermediate stations, each of which may receive all the signals 
quite as well as the terminal station. But since the intensity of 
the current decreases rapidly, as the distance from the battery in- 
creases, in consequence of the imperfect insulation of the wires, 
Morse’s ingenious application of a local circuit is used, that these 
signals may be distinctly registered. Ee 
_ Fig. 2 represents a station on the main line. The significa- 
tion of the letters is the same as in fig. 1, the key K regulating 
’ the spring. The armature-beam C is connected with one electrode 
of the local battery, the other being connected with the metallic 
inner stop I. An attraction of the armature closes the local cir- 
cuit, on which is the recording apparatus, and thus a very weak 
current may suffice to close the circuit of the local battery, which 
» regulated to any degree of intensity required. 
; HOW suppose that at one extremity of a long circuit the 
um of aclock is made to interrupt the current for a mo- 
