Loseby’s Isochronal Spring

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Loseby’s Isochronal Spring

This topic has 26 replies, 3 voices, and was last updated 28 July 2023 at 14:46 by david bennett 8.

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23 July 2023 at 16:50 #653409
david bennett 8
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@davidbennett8
Has anyone noticed this? I came across it in my pdf copy of Grimthorpe's Clocks Watches and Bells on pages 63/4. There is a very brief description. It seems to be a very simple single loop of spring wire loosely embracing the pendulum rod so that over-impulsing would cause the rod to stretch the loop. This device was exhibited in 1851 and at first the Astromer Royal said it worked. Then Grimthorpe intervened on the grounds that escapement errors had the opposite effect. The AR did some more experiments, then dismissed the spring.

Now that the trend is towards removing the escapement and it's errors, is it time to re-visit this? Does anyone have any detail of it's construction? If it is any use it could easily be retro-fitted to any pendulum.

dave8
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23 July 2023 at 16:50 #4026
david bennett 8
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@davidbennett8
23 July 2023 at 17:25 #653414
Michael Gilligan
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@michaelgilligan61133
Thanks for the reference

I felt sure that I had a PDF on the iPad, in GoodReader … but couldn’t find it

Downloading it again revealed the file name and all is now well.

MichaelG.
23 July 2023 at 18:03 #653426
John Haine
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@johnhaine32865
This kind of arrangement has been invented more than once to correct for circular deviation.
23 July 2023 at 18:39 #653428
david bennett 8
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@davidbennett8
Posted by John Haine on 23/07/2023 18:03:26:

This kind of arrangement has been invented more than once to correct for circular deviation.

John, after much unsuccessful searching, can I ask if you have any references?

dave8
23 July 2023 at 21:18 #653441
Michael Gilligan
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@michaelgilligan61133
Brief mention of Loseby’s device here: **LINK**

Loseby Reasearch

MichaelG.
23 July 2023 at 21:57 #653442
david bennett 8
Participant
@davidbennett8
Thanks Michael.Yes, I had seen that sad story. The British Museum suggested a couple of books. Nothing in Brittans, I dont have access to the Loomes clockmakers list.

dave8
23 July 2023 at 22:59 #653448
Michael Gilligan
Participant
@michaelgilligan61133
One, somewhat confusing, image here: **LINK**

https://www.bridgemanimages.com/en/search?filter_text=1851%20great%20exhibition%20loseby’s&filter_group=all&filter_region=GBR&sort=best_relevance

MichaelG.
24 July 2023 at 02:29 #653463
david bennett 8
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@davidbennett8
Michael, thanks. The link didn't work at first until I re-entered the search with inverted commas. I take it it's the engraving of a mercury compensated pendulum with what could be the spring?

dave8
24 July 2023 at 04:21 #653465
Michael Gilligan
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@michaelgilligan61133
Indeed, Dave

Sorry … I hadn’t noticed the ascii error …

MichaelG.
24 July 2023 at 04:33 #653466
david bennett 8
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@davidbennett8
Thats ok. I have found it with explanation on internet archive. Its " The practical mechanics journal" vol 5 dated 1853. The explanation is not much more than can be guessed at from your pic.

dave8

Edited By david bennett 8 on 24/07/2023 04:34:18
24 July 2023 at 13:41 #653518
david bennett 8
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@davidbennett8
Posted by david bennett 8 on 24/07/2023 04:33:52:

Thats ok. I have found it with explanation on internet archive. Its " The practical mechanics journal" vol 5 dated 1853. The explanation is not much more than can be guessed at from your pic.

ps – page31

dave8
24 July 2023 at 14:14 #653524
John Haine
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@johnhaine32865
David,any chance you could post an image of the relevant page or a direct link please?
24 July 2023 at 18:28 #653549
david bennett 8
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@davidbennett8
John, willl try -the file is too large

dave8
24 July 2023 at 19:24 #653555
david bennett 8
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@davidbennett8
https://books.google.co.uk/books?id=B9pQAAAAYAAJ

Hi John, see if this works

dave8
25 July 2023 at 14:01 #653639
david bennett 8
Participant
@davidbennett8
https://books.google.co.uk/books?id=nDxWAAAAcAAJ

John, have just found this better account of Loseby's compensator

dave8

Edited By david bennett 8 on 25/07/2023 14:26:30
25 July 2023 at 14:20 #653641
Michael Gilligan
Participant
@michaelgilligan61133
Well done, Sir

… tucked away quietly after his masterly ‘secondary compensation’ of the Chronometer Balance

MichaelG.

.

https://books.google.co.uk/books?id=nDxWAAAAcAAJ

Edited By Michael Gilligan on 25/07/2023 14:25:43
25 July 2023 at 18:52 #653689
John Haine
Participant
@johnhaine32865
Thanks Michael and Dave. Similar in principle to methods proposed by others except Loseby was first and certified by Airy no less! I will try to dig out the other references I've seen.
26 July 2023 at 12:15 #653773
John Haine
Participant
@johnhaine32865
The other key reference on this is by Bush and Jackson "Correction of spherical error of a pendulum" in

Journal of the Franklin Institute

Volume 252, Issue 6, December 1951, Pages 463-467

alas only available if you pay or have institutional access. Vannevar Bush was an eminent US science maven in WW2 and after who played a major role in things like early computers etc. Also interested in clocks and there are a couple of articles in Scientific American describing their experiments dating from the early 1960s. The article above has a reference to Loseby but he only had the rather negative Grimthorpe reference and hadn't seen the Practical Mechanics stuff and the test report by Airy. The scheme used a tension spring pulling downward on a point on the pendulum, the other end being held vertically below the point of suspension. As the pendulum swings the spring is slightly stretched and the geometry can be designed to provide an additional restoring force proportional to the cube of the angle that can cancel the cubic term of the sinusoidal restoring force. In practice they used a cantilever leaf spring at right angles to the pendulum with a thin wire connecting it to the pendulum rod. Good results are reported, I haven't compared them with Airy's measurement yet.

As far as I can see Loseby's spring creates the cubic dependency through its shape and from my brief look at the description he doesn't say what this has to be mathematically. By contrast Bush only assumes that the spring is linear (a good approximation for small extensions) and the cubic term comes from the geometry.
28 July 2023 at 08:51 #654067
John Haine
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@johnhaine32865
Michael was asking for more details of my claim of other mentions of a similar technique.
- Loseby's approach actually only applies the correcting force over a small part of the arc on one side.
- Bush/Jackson aim to exactly correct for the cubic terms at least for small deflections.
- The Bulle clock included a coil spring arranged in a very similar way to Bush's to keep period constant as battery voltage declined, in the early 20th century.
- David Robertson described the theory of the Bush type compensator in 1929 in one of his classic HJ articles.
- IIRC Peter Hastings described a scheme a bit like Loseby's in HJ a few years ago.
28 July 2023 at 09:16 #654070
Michael Gilligan
Participant
@michaelgilligan61133
Posted by John Haine on 28/07/2023 08:51:47:

Michael was asking for more details of my claim of other mentions of a similar technique.

[…]

.

really ? … I thought it was dave8

MichaelG.
28 July 2023 at 09:56 #654074
John Haine
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@johnhaine32865
Oops! Apologies both.
28 July 2023 at 09:58 #654075
Michael Gilligan
Participant
@michaelgilligan61133
No problem, John

MichaelG.
28 July 2023 at 11:23 #654087
david bennett 8
Participant
@davidbennett8
Thanks John. I must note that your first point is entirely in line with Loseby's aim of his correcting force "to only act through that part of the arc in which it was required". Are there any quantative results on the performance of the other attempts you mention? ( I am not expecting results on the basis of a 4:1 change of driving force as in Airy's tests.)

dave8
28 July 2023 at 12:06 #654096
John Haine
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@johnhaine32865
Yes, Bush and Jackson report test results. I'll post them later.
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