Francis Mathews Green

“ The latitude of any point being determined directly by observation, and independently of the latitude of any other place, is less likely to be in error than the longitude, which can only be ascertained with reference to the meridian of some other place; being measured by time, is determined by the comparison of the local time with the time at some other place, the longitude of which is known. ”

“ By means of these instruments, the error of the chronometer is found at each station with great accuracy, and, the times shown by the faces of the chronometers being compared by telegraph, the difference of time and corresponding difference of longitude are readily deduced.
The time occupied by an electric impulse to traverse the wire from one station to another, and act upon the telegraph-instruments, though generally very small, is too great to be neglected, but is easily ascertained and allowed for. ”

“ In connection with their preparations for observing the recent transit of Venus, German astronomers have made some telegraphic measurements of differences of time in the East Indies; but the vast and constantly increasing net-work of cables nearly surrounding the earth will afford work for years to come, and will, in a way hardly contemplated by the projectors, add in a very great degree to accurate geographical knowledge. ”

“ A little carriage, to which a pen of peculiar construction is attached, moves upon wheels along the cylinder in the direction of its length, about one-tenth of an inch for each revolution of the cylinder, so that the pen records a perpetual spiral. ”

“ By means of a little instrument called, a break-circuit key, in the hands of the observer, and included in the same circuit, the electric current may be interrupted, causing the pen to make a similar mark as shown at b, on the occurrence of any event, such as the passage of a star across the wires of the telescope. ”

“ In order that the work might be accomplished with economy, as small a vessel as possible was desirable, the Fortune, a strong iron tugboat of 300 tons, being selected and prepared. Although this little vessel carried the officers and men of the expedition safely, she was found to be too small to encounter heavy weather at sea with any degree of comfort. ”