telegr aph. 
72 Kee et the Galvanic Currentin Telegraph Wires. 
onaies at each oscillation, the circuit being restored immediately 
afterwards as before. We shall have on the registers of the sev- 
eral stations a series of lines alternating with pauses or blank spa- 
ces,—dots, as they are called, in the technical phraseology of the 
If the fillets were moved forward with a uniform velocity by 
the machinery of the registering apparatus, and no changes oc- 
curred in the intensity of the current in the wire, each of the 
lines upon any one fillet would be of the same length,—as also 
would each of the pauses. And if the velocity given to the fil- 
lets at the several stations were the same, the lines representing 
seconds would be of one length on all the registers. la 
we cannot expect, nor is it in any manner necessary, for it isan 
easy matter to reduce all the registers toa uniform scale. But 
that the motion of each single fillet be uniform is very desirable. 
To obtain a near approximation to such uniformity requires ma- 
chinery far more delicate and more carefully constructed than that 
which is in use in the telegraph offices, and with which the ex- 
periments of the Coast Survey have been made. Such apparatus 
has been devised and is constructing by Mr. Boyden of Boston, 
and by Mr. Bond of the Cambridge Gbaberanaes It forms also 
an essential part of the apparatus of Prof. Mitchel. Yet, as we 
are in fact dependent on the rate of the driving machinery of the 
registering apparatus only for a single second in each case, the 
use the mean of a number of cases, instead of isolated observations. 
At each station on the line of telegraph, during the experi- 
ments for velocity, a contrivance is introduced into the wire cil- 
cuit, of such a kind, that the cirenit may be broken by pressing 
upon a key, which is restored by a spring to its original position 
as soon as the pressure is removed. One of these ‘“ break-cireuit” 
keys is represented at G (fig. 1). It is ee in te power of the 
operator at any station to break the cireuit whenever he chooses; — 
and in this way to communicate at once with all other stations on 
the line. : 
After a galvanic battery and the circuit-breaking clock have 
been connected with the line, we have at each station, a clock 
scale, that is, aseries of lines, separated by short pauses, each 
pause corresponding to the beginning of a second, whose dura- 
tion is denoted by the length of the grooved line. In the clock 
of this kind at Washi pgton, that pause is omitted which corres 
ponds to the begim of each minute, and this enables us 
iden tify ona fillet from any station, the cheer use. 
* 
