Hi Brad,
Perhaps we are working at cross purposes here, or misunderstand each other. I am not trying to correct Worsley's work, but rather have sought to simply explain the working of his sight for Longitude and his methodology of calculating his CE therefrom, and thereby to demonstrate to the List in general how this was done historically.
It was my understanding that both you and George were not factually aware of the actual position from which his observation was made and that the selection of Point Wild was an assumption, calculated or otherwise - if I am wrong then of course Worsley appears to have made a mistake or we misunderstand the true meaning of his 1 min + 4 sec. DLo.
I have simply played the part of the devil's advocate in, without his confirmation of the observation site, considering him to have been too good a navigator to have misstated the DLo between that site and his knowledge of the position of Cape Belsham. I have tried to express the opinion, perhaps clumsily, to the effect that, without a factual knowledge of his observation site position and his knowledge of the position of Cape Belsham at the time, we are unable to assess the accuracy of his work in the context of 1916. This in no way seeks to express an opinion with respect to the "what if" as respects the now known position of Cape Belsham and Point Wild or how this may have affected his subsequent movements.
Perhaps time was of the essence, however, in like circumstances it perhaps may have been more appropriate to have waited a sufficient time to have confirmed the CE and position by additional observations over a longer period of time.
Regards,
Henry
- On Tue, 3/24/09, bmorris@tactronics.com <bmorris@tactronics.com> wrote:
From: bmorris@tactronics.com <bmorris@tactronics.com> Subject: [NavList 7748] Re: Transcription of Worsley's Log To: NavList@fer3.com Date: Tuesday, March 24, 2009, 1:26 AM
Hi Henry
After a tremendous amount of typing, I finally saw what you were saying and started over. We agree, Worsley saw his longitude as West 54-50-00 and we think, based on modern charts, that the longitude is West 54-53-45. This gives us a delta longitude of 00-03-45.
So why does my 2.13 not agree with your 1.804? I used a great circle distance, accounting for the difference in latitude as well as the distance in longitude. Your calculation, I believe, accounts only for the DLO. Fundamentally, these values are fairly close and not truly worthy of extended discusion.
---------------- This is the point I am trying to drive at, however. If his observation and consequent reduction yields West 54-19-45 and he "knows" West 54-50-00, then his DLO is 00-30-15 (arc). If we convert this arc to time, we should get 2 minutes 1 second of CE, not 1 minute 4
seconds. This is where I would like a bit of help in my understanding.
I think from your equations of the other day that {you think} he estimates his distance to Cape Belsham at 1 minute 4 seconds (time) and therefore he must subtract that out from his CE. That supposes that there are 16 minutes of arc to Cape Belsham from Point Wild. That is very high of the mark. He can see it from Point Wild pretty clearly. I measure it on my chart 29104 at 00-01-30 arc. So 1 minute 4 seconds time should really be much lower, or roughly 6 seconds time.
Thats a 58 second delta. If you read Worsley's note on 7 May 1916, he states that he is "about" 20 miles astern due to his CE, on an easterly course. So even Worsley knows his chronometer is slower than he expected.
This can be attributed to (1) Worsley doesn't have a good idea of the rate of his chronometer. (2) Worsley doesn't get the right value
for CE on Elephant Island.
Which one? I simply don't know. I find both outcomes strange. He should know the rate of his chronometer after working with it on this expedition. Maybe he just started working with this pocket chronometer after abandoning all others on the ice. He also knows the longitude of Cape Belsham fairly well (not to modern values, but not too far off).
------------------------------------------- Your calculation was
Meridian angle 02-55-24.6 East (in time) 11-59-60 LAT 09-04-35.4 GAT 12-41-54
Longitude 03-37-18.6 W (time) = 54-19-39 W (arc) DLo Cp Belsham 00-01-04.0 W (time) = 00-16-00 W (arc) Calc Lo Cp Belsham 03-38-22.6 W (time) = 54-35-39 W (arc) True Lo Cp Belsham 03-39-32.2 W (time) = 54-53-02 W (arc) Diff = CE, Slow 00-01-09.6 (time) = 00-17-23 (arc)
The "Dlo Cp Belsham" is too large. It should read 00-00-06 W(time)=00-01-30 W (arc).
Another very minor point, the "True Lo Cp Belsham" should read 54-50-00, not 54-53-02 (thats the modern value). This would reduce the time downwards from 00-01-09.6.
---------------------
I do appreciate your time on these points Henry. It is helping me to get this right!
Best Regards Brad
Morris
--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
|