Loseby's Isochronal Spring

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

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.

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

Brief mention of Loseby’s device here: **LINK**

http://www.thetimeworkshop.uk/loseby-reasearch/

MichaelG.

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

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.

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

Indeed, Dave

Sorry … I hadn’t noticed the ascii error …

MichaelG.

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

ps - page31

dave8

David,any chance you could post an image of the relevant page or a direct link please?

John, willl try -the file is too large

dave8

https://books.google.co.uk/books?id=B9pQAAAAYAAJ

Hi John, see if this works

dave8

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

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

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.

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.

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.

.

really ? … I thought it was dave8

MichaelG.