Member postings for Michael Gilligan

Looks like a good acquisition

… if I understand your question correctly, the diaphragms should be aligned on the same optical axis.

That said; people do like playing around with offset lighting !!

A photo or two of the set-up would help.

MichaelG.

Edited By Michael Gilligan on 05/09/2023 14:06:45

I have three bags of these pears, each containing Qty.4

Although I have not weighed them, all twelve pears look ‘reasonably’ interchangeable

This bag has the marking 1:3 but the others are marked 1:4

… I know not what that means

MichaelG.

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Presumably because they are Tesco

…. and possibly so that they can claim their pears are bigger than typical

MichaelG.

I will photograph the plastic bag later !

Sorry … I thought I had been sufficiently explicit about what was, and was not, stated thereon.

MichaelG.

Fair comments, both

But the weight is explicitly stated [not an ‘average’ or ‘approx’ in sight]

they also give a size range of 58/68mm and note that ‘This pack contains a minimum of 4 pears’

It just seems strange and is engineering-ish, as befits the Tea Room

MichaelG.

[ For the sake of our Moderators … please keep this technical ! ]

I recently bought some Conference Pears from Tesco

These are imported from Belgium and the standard pack weighs 610g

… The obvious question being … Why ?

I’m sure we are all familiar with ‘Metric’ weights of 454g and 227g but I cannot see anything special about 610

MichaelG.

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Just for clarity, Jeff … he actually wrote: about 2" long by 1/2" wide

no mention of thickness

MichaelG.

Edited By Michael Gilligan on 05/09/2023 06:55:59

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It happens … The first An earlier thread on this topic, in which I posted a link to the [technical] Loughborough reporting was “disappeared” entirely.

MichaelG.

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[edited to correct my unproven supposition]

Edited By Michael Gilligan on 05/09/2023 04:38:27

I give up

You have not misunderstood, Ian

… this the optical equivalent of ‘tramming’

MichaelG.

Edited By Michael Gilligan on 05/09/2023 04:16:27

There is more detail about it here:**LINK**

https://opg.optica.org/boe/fulltext.cfm?uri=boe-9-8-3624&id=395204

MichaelG.

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Agreed, Duncan … that’s the very essence of it.

There’s a difference between ‘a cycloid’ and ‘the appropriate cycloid’

MichaelG.

Another useful item [if you happen to need one] is a ‘water level’ complete with 15m of tube for £4.99

MichaelG.

.…. and therefore, to a roller of zero radius [i.e. an hypothetical knife-edge]

MichaelG.

But do you have any suggestion what they might be ?

MichaelG.

Looks like they could be part of a centrifugal clutch mechanism

MichaelG.

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In which case, everything I have written so far is wasted effort

Please ignore me

MichaelG.

Good morning, Dave

For the sake of your sanity, [and mine] … I will try once more, in bite-size steps:

1. Galileo told the world that the pendulum was isochronous … this [the story goes] being based on his personal observation of either a large thurible, or a lamp, in Pisa cathedral … the timing of which he checked with his pulse [!]
2. This was over-simplistic
3. Huygens put things right; by demonstrating that a simple pendulum was not isochronous, but that it could be made so by forcing it into cycloidal motion.
4. Please note that the hypothetical ‘simple pendulum’ comprises a massless and infinitely flexible ‘string’ hanging from a rigid support, and carrying a heavy bob of zero physical dimensions. [Reality is, of course, a little different]
5. Huygens’ clock used a verge escapement, which nicely suits the large angle of pendulum swing.
6. As horology developed, the anchor escapement and the dead-beat escapement superseded the verge, and the pendulum became a rod and bob, suspended on a ‘spring’ of shim.
7. This arrangement is not intrinsically isochronous, but can be considered so at the small angles of swing which suited the new escapements.
8. Further attempts to improve isochronism, by introducing cycloidal cheeks proved futile, because they could only act on the suspension spring … and that made appropriate dimensioning impractical … The problems far-outweighed any improvement.
9. Fedchenko saved the day with his astonishing spring arrangement, but that’s another story.
10. Your proposed roller arrangement, as the support for a rodded pendulum, cannot possibly mimic Huygens’ purist analysis …

I can only suggest that you work-through the clear instructions provided by Huygens, to get a ‘feel’ for the geometry.

MichaelG.

You make a good point about ‘the media: Alan …

Jeremy Hunt gave a calm and measured performance when interviewed by Laura Kuenssberg yesterday morning, but then the reporting by the Independent last evening sensationalised it.

MichaelG.

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But that’s surely on an axis rotated 90° from what is normally considered a knife-edge suspension

… sorry, I’m too confused to think it through

MichaelG.

Edited By Michael Gilligan on 03/09/2023 21:32:40