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Hi Fred:

I'm not knowledgeable about the specifics of the telegraph system, but I
would think that the drum recorder could be used to characterize the
relay (repeater) delay quite easily.  Then knowing the exact route of
the line sum all of these.  I would expect the delay in a good relay to
be less than 20 milliseconds.

Happy Holidays,

Brooke Clarke, N6GCE
http://www.PRC68.com

Fred Hebard wrote:

> Brooke,
>
> Thanks.  I was wondering about propagation delays engendered by relays.
>  My imperfect understanding is that these were used every hundred miles
> or so, and were the big breakthrough Morse obtained from Henry that
> permitted a practical telegraph system.  But it's unclear to me the
> separation needed between relay stations and their switching time.
>
> Fred
>
> On Dec 26, 2003, at 2:27 PM, Brooke Clarke wrote:
>
>> Hi:
>>
>> My reading is that the key element was replacing ears trying to
>> interpolate between one second ticks and the use of a drum recorder
>> with
>> a tick recorded once per second where interpolation could be used to
>> determine the time of star crossings that were also marked on the drum
>> by an observer pressing a manual key while looking through a 48"
>> meridian transit.
>>
>> In this scenario with a 1,000 mile separation between stations the
>> propagation delay would be on the order of 5 milliseconds which is
>> probably in the noise compared to the human reaction time variation in
>> pressing the key.  But could be calculated based on the known
>> propagation constant for the open wire type lines then in use.
>>
>> Happy Holidays,
>>
>> Brooke Clarke, N6GCE
>> http://www.PRC68.com
>>
>> Fred Hebard wrote:
>>
>>> I have read this article carefully, and methods for determining the
>>> propagation delay in the circuit are not readily apparent to me.  If
>>> an
>>> astronomic phenomenon that occurred simultaneously at both sites were
>>> measured, the delay could be determined, it appears to me.  Perhaps
>>> occultations of Jupiter's moons might be free of parallax effects?
>>> Also, it would seem for the measurement of a simultaneous effect that
>>> the sites might need to be connected by two circuits.
>>>
>>> On Dec 24, 2003, at 2:32 PM, Fred Hebard wrote:
>>>
>>>> Thanks Paul!  I had been wondering how they got around propagation
>>>> delays.
>>>>
>>>> On Dec 24, 2003, at 2:14 PM, Paul Hirose wrote:
>>>>
>>>>> Professional Surveyor magazine has an online article about the early
>>>>> use of the telegraph for longitude determinations.
>>>>>
>>>>> http://www.profsurv.com/ps_scripts/article.idc?id=1147
>>>>>
>>>>> Alexander Bache, head of the U.S. Coast Survey, was quick to realize
>>>>> the possibilities. He organized an experiment which measured the
>>>>> longitude difference between Washington and Philadelphia by means of
>>>>> telegraph in 1846.
>>>>>
>>>>> By the mid-1850s, the technique had become routine. Chronographs
>>>>> recorded the electrical impulses of the observer's hand switch on a
>>>>> paper-covered rotating drum as stars crossed the meridian at both
>>>>> observatories. Also recorded were 1-second pulses from break-circuit
>>>>> chronometers at both ends of the telegraph line. With this data,
>>>>> surveyors could eliminate clock offsets and propagation delays.
>>>>>
>>>>> Telegraphic longitudes were a huge improvement over the Coast
>>>>> Survey's
>>>>> former longitude methods: lunar culminations, lunar occultations,
>>>>> and
>>>>> chronometer transportation. (Before the trans-Atlantic cable was
>>>>> laid,
>>>>> the Survey made more than 1200 chronometer exchanges with England.)
>>>>>
>>>>
>>>
>>>
>>> ----------------------------------------------------------------------
>>> --
>>> Frederick V. Hebard, PhD                      Email:
>>> mailto:Fred@acf.org
>>> Staff Pathologist, Meadowview Research Farms  Web: http://www.acf.org
>>> American Chestnut Foundation                  Phone: (276) 944-4631
>>> 14005 Glenbrook Ave.                          Fax: (276) 944-0934
>>> Meadowview, VA 24361
>>>
>>>
>>
>
>

   

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