Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Time sights
    From: Lu Abel
    Date: 2005 Jun 1, 20:30 -0700

    Gentlemen:
    
    The first cable was plagued with inadequate insulation, resulting in
    frequent bouts of not quite short circuits but signal losses so great
    that telegraphic characters were often simply not received at the far
    end.  It was this that led to it requiring "several hours" to transmit a
    telegram.
    
    "Spreading" of electrical signals takes place when a medium (such as a
    cable) can not transmit the high frequency portion of a signal.  An
    on-off pulse, such as a telegraphic character, theoretically includes
    signal components of very high (indeed, infinite) frequencies.   But the
    speed of transmission is still the speed of light.  Thus a nice sharp
    pulse transmitted on one end of the cable might arrive as a smeared-out,
    possibly unrecognizable mess -- but it would travel across the Atlantic
    (and therefore arrive) in a fraction of a second.
    
    There were actually two trans-Atlantic cables laid.  The first worked
    only for a few months due to the insulation problem.   I don't recall if
    an attempt was made to transmit well-timed signals over it to verify
    latitude, but it would seem a very obvious thing to do.
    
    The second cable had adequate insulation and worked until better
    technologies forced its replacement.  I'm certain that time signals were
    transmitted over it.
    
    Lu Abel
    
    Alexandre Eremenko wrote:
    > Fred,
    > What I wrote is not COMPLETELY incorrect:-)
    > The time spread of signals DID happen.
    > And the first short telegram sent DID take
    > several hours to transmit (I don't remembr, 6 or 12 hours,
    > but of this order of magnitude).
    > That they sooner or later found some way to overcome this
    > difficulty might be true. But I doubt they knew how to do it
    > at the time they layed the cable.
    > Alex.
    >
    > On Wed, 1 Jun 2005, Fred Hebard wrote:
    >
    >
    >>Actually, this is completely incorrect.  One of the first things done
    >>with the first transatlantic cable was to transmit time signals to
    >>determine more accurately the difference in longitude between North
    >>America and Europe.  There are ways of transmitting signals both ways
    >>to account for the various delays.  Paul Hirose was kind enough to tell
    >>us how this was done a few years ago; unfortunately, I didn't
    >>understand the mechanism well enough to reproduce it here.
    >>
    >>Fred
    >>
    >>On Jun 1, 2005, at 11:28 AM, Alexandre Eremenko wrote:
    >>
    >>
    >>>I can suggest another reason why time transmission though
    >>>a transatlantic (or other very long) cable could not be acceptable.
    >>>In those XIX century cables,
    >>>the signals were substantially spread in time
    >>>when transmitted.
    >>>For example, in the very first transatlantic cable,
    >>>a short message of few words had to be transmitted
    >>>for several hours. A sharp impuls you send from one end
    >>>arrived as a very long wave.
    >>>So reliable transmission of a time signal could be
    >>>impossible.
    >>>Alex.
    >>>
    >>>
    >>>On Wed, 1 Jun 2005, Fred Hebard wrote:
    >>>
    >>>
    >>>>In reading the Wikipedia entry on celestial navigation, I came across
    >>>>the following statement:
    >>>>
    >>>>"Traditionally, a navigator set his chronometer from his sextant, at a
    >>>>geographic marker surveyed by a professional astronomer. This is now a
    >>>>rare skill, and most harbor masters cannot locate their harbor's
    >>>>marker."
    >>>>
    >>>>A few years ago, in discussing a late 19th-century book about repair
    >>>>of
    >>>>submarine telecommunications cables, I asked why the captain and first
    >>>>mate went ashore to do time sights, when the could have gotten time
    >>>>from the cable.  I suppose the answer was that time wasn't sent over
    >>>>the cable that often, not to mention that it might have been broken
    >>>>when they were in harbor.  At any rate, this is the first mention I
    >>>>have of people setting their chronometer from a precisely measured
    >>>>location.  Previously, I had gather from this list that the captain
    >>>>and
    >>>>first mate were rating their chronometer, not setting its absolute
    >>>>time.  It appears they were setting it, and perhaps also rating it.
    >>>>
    >>>>Is there any mention of this in the older texts, such as Chauvenet,
    >>>>where time sights were done at geographic markers set by a
    >>>>professional
    >>>>astronomer?
    >>>>
    >>>>Thanks,
    >>>>
    >>>>Fred
    >>>>
    >>>
    >
    >
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site