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On April 22, 1861, Andrew Carnegie--yes, that Andrew Carnegie--telegraphed the Telegraphs Superintendent of the Pennsylvania Railroad at Altoona, Pennsylvania as follows: "Send four of your best operators to Washington at once, prepared to enter a newly created Government telegraph service for the war." Those four operators were the original operators of the United States Military Telegraph Corps, an organization that would grow to over 1500 men. One of those four men was 18-year old David Homer Bates. He chronicled his service in the Corps and almost daily close contact with President Lincoln in his wonderful book, Lincoln in the Telegraph Office (1907).

Bates' diary is in the Rare Book and Special Collections Division of the Library of Congress.
(http://lcweb2.loc.gov/cgi-bin/ampage?collId=rbc3&fileName=rbc0001_2012stern00012page.db&recNum=0)
A published transcription of the diary with copious notes was published as The Telegraph Goes to War (2003), edited by Donald E. Markle. I've just finished a transcribed version for the LOC; that version (that corrects several of Markle's transcription errors and includes all of the personal material that Markle omitted should be available for online text searches in the not too distant future.

The Saturday, February 27, 1864 entry in Bates' diary reads: "Prof. Dean came to the office this evening to experiment with Gauley Bridge [located south of Charleston, West Virginia], a distance of nearly six hundred miles, worked with him very successfully. Exchanged signals 8 or 10 times each." 
(http://lcweb2.loc.gov/cgi-bin/ampage?collId=rbc3&fileName=rbc0001_2012stern00012page.db&recNum=78)

Markle notes that "Professor Dean is not further identified." Penciled just above this entry, however, appears the word "Longitude!"

I've been interested in longitude for a few years now, probably since Dava Sobel's book was recommended to me years ago (and I became re-interested in telegraphy about the same time). I was puzzled by this penciled-in note and tried to track down this Prof. Dean. He turned out to be George Washington Dean, born in 1825; he had "joined the [US] Coast Survey at the age of twenty-one and would spend the next thirty-eight years pursuing the elusive longitude (Longitude by Wire: Finding North America, by Richard Stachurski)." Indeed, just two weeks after Morse's first telegraph exchange between Washington and Baltimore, the difference in longitude between the Capitol in Washington and the Battle Monument Square in Baltimore, was determined to be "1 minute 34.868 seconds of time (according to Stachurski)," calculated by averaging the time delay in telegraphic signals between the two stations.

This and many other interesting stories chronicling the intersection between telegraphy, geodectic survey, and astronomy in the mid-to late 19th century can be found Stachurski's richly detailed and fascinating book.

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Dale/KJ4VTS
38° 56’ N
77° 19’ W