Telegraphic Determinations of Longitude. 23 
ments constituted the final links in a long chain, extending from 
the prime meridian Greenwich across the Atlantic to the United 
States, thence via the West Indies to Panama, down the west 
coast of South America to Valparaiso, across the Andes to Cordova 
and Buenos Ayres, up the east coast to Pernambuco, across the 
Atlantic to Lisbon, and thence to Greenwich, altogether a distance 
of eighteen to twenty thousand miles. The two longitudes of 
Cordova, as brought from Greenwich by the two routes, differed 
from each other by only 0%.048, a result which speaks well for the 
accuracy of the methods employed. When preparations were 
being made for this expedition, it was determined to accomplish 
if possible. something in the way of getting rid of the personal 
equation in exchanging signals. An idea which had been sug- 
gested by work done by Major Campbell, R. E. in the measure- 
ment between Bombay and Aden, seemed to promise well. It 
was to be used with the siphon or other form of recorder. The 
ordinary double current cable key with two levers, was arranged 
with an additional lever in such a manner that while in ordinary 
use in the telegraph office, it could also be put in circuit with the 
chronometer and chronograph in the observatory, and a signal 
sent through the cable would have its time of sending registered 
on the chronograph. Ordinarily in speaking over a cable line, 
connection is made in such a way that the current sent does not 
pass through the recorder at the sending station, as a violent 
movement of the siphon would result. By means of a shunt, how- 
ever, it is possible to control this movement somewhat. Suppose 
now, that the connections at each station are made in such a way, 
by means of this key and the shunt, that a signal sent from one, 
is registered on both recorders and on the sender’s chronograph. 
The observers leaving their assistants to take care of the chrono- 
graphs, go to. the respective telegraph offices, and all being ready, 
the observer A taps his key. This sends an impulse through the 
cable, which appears on A’s recorder, as a violent jump or kick of 
the siphon. On B’s recorder it is registered as a deflection like 
the ordinary dot or dash, at the same instant is recorded on A’s 
chronograph the time of sending. As soon as B sees the signal 
on his recorder, he taps his key also registering the signals on 
both recorders and on his chronograph. A, seeing B’s signal again 
taps his key, and so on, as long as desired. The result is that 
each observer has a record on his siphon fillet of all signals sent 
and received, while the times of those he sent are recorded on 
