Telegraphic Determinations of Longitude. 9 
easily recognized. These instruments served their purpose very 
well, but had several disadvantages. The rate of movement of 
the paper was not regular; when the clock-work was first wound 
up the motion was rapid and the second spaces long, and as the 
spring ran down the marks became shorter and shorter. Another 
drawback was the great length of the fillet ; with spaces only an 
inch in length, it required five feet of paper to record a minute 
in time, and after a night’s observation, there would be several 
hundred feet to examine, measure and record, occupying the 
greater part of the following day. By stopping the instrument 
between the observations something was gained in this respect, 
but this tended somewhat to confusion and error in keeping the 
record. They were only used for one season’s work, and in their 
stead were procured two cylinder chronographs, made by Bond 
of Boston. These were fine instruments, but somewhat too 
delicate to stand the necessary transportation. In these imstru- 
ments as in most other chronographs, a cylinder about six inches 
in diameter is made to revolve by clock-work once in a minute. 
An electro-magnet mounted on a carriage actuated by the same 
clock-work moves alongside the cylinder, in a direction parallel 
with its axis, at the rate of about an eighth of an inch in a minute. 
The armature of the magnet carries attached to it a pen, the point 
of which rests upon a sheet of the paper wrapped around the 
cylinder. While the circuit through the coils of the magnet is 
complete, the pen makes a continuous spival line upon the paper, 
but when the circuit is broken by the chronometer, or key, it flies 
to one side making an offset, and immediately returns to its 
position, as soon as the circuit is again closed. The result is to 
graduate the whole surface of the paper into second spaces, from 
which the observations can be read off with the greatest ease. 
For supplying the electric current, there was used at first, a 
modification of the Smee battery, but this proving very uncertain 
in strength, a gravity battery was substituted, and afterwards a 
number of LeClanché cells were procured. 
Upon the first expedition, no telegraph instruments were car- 
ried, but the use of such as were needed was easily obtained from 
the telegraph companies. The line between Aspinwall and 
Panama was in good condition and no trouble was experienced in 
exchanging the time signals by which was effected the compari- 
son of the chronometers. Wires were stretched from the observa- 
tories in each place to the respective telegraph offices, and for 
