Speculum metal is a mixture of around two-thirds copper and one-third tin making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to optical devices until it was replaced by more modern materials such as metal-coated glass mirrors. from Wikipedia.
Fascinating for an amateur optician and telescope maker, such as myself. Possibly a Huygens eyepiece, the first compound type, invented in the 1660's, although usually the lens closer to the eye is smaller than the one closest to the mirror. Those speculum mirrors tarnished fairly quickly and re-polishing them also meant one had to simultaneously re-figure them to the correct curvature (as Rayleigh's Rule later showed, a spherical section is usable at f ratios of f8.2 or greater for a six inch mirror, as this example seems to be, and can be figured fairly easily when polishing with a pitch lap and optical rouge...for shorter focal ratios it has to be paraboloidal to eliminate spherical aberration...a far harder shape to figure and test for on larger mirrors, such as those used by Sir William and Caroline Herschel) - source: Jean Texereau's seminal work on amateur telescope making, "How to Make a Telescope", 1957. The book I followed to make my first Newtonian reflector back in 1966 when I was 14 years old.
My only objection to that was Keith's description of them as children's books. I read them as an adult, suffering insomnia, waiting for my sick father to pass. But they are fantasy, with no connection to the real world.
@@UncleKennysPlace That was just an amusing little barb to characterize that master-student dynamic they use to explain things on camera. Don’t worry about it :)
Great to see this. This was very high end for its time and speculum mirrors got bigger and bigger, however, they were hard to fabricate and maintain and lost their reflectivity quite quickly; then in the 1850's someone invented silver on glass mirrors and that became the next big leap in telescope design. Glass is much easier to fabricate than speculum, the slivered coating stays shinny for much longer, and speculum became obsolete.
Wonderful! So Hadley’s telescope preceded William Herschel’s and must have served as a design model for Herschel to use when making his reflectors? Thanks for the video! More astro artifacts please!
Who could have borrowed an object for ~87 years, did the object remain in his/her possession until now. And did the Royal Society know where the object whereabouts in the past 87 years or did they thought it has gone missing 🤔
Brady making a selfie with the mirror Meanwhile the guy about to invent a device that reads the mirror's atoms and recreate the actual images of Saturn...
I watch a huge number of science/skeptic videos on RUclips, and yet RUclips has never "recommended" one of your videos to me. I came here via Captain Disillusion on Twitter. Check your SEO? (happy to be here, BTW)
Yep. Speculum is also the name of the metal alloy that the mirror is made from 0:53. The name comes from the Latin 'speculum' meaning a mirror or reflector. I don't know if the medical instrument was at some time made from this metal or if the name perhaps comes from the Latin 'specere' meaning to look at or to view. I feel smarter for googling that ;)
Props to James for immediately getting the focus just right on the tiny Brady in the eyepiece
Haha - thanks! :)
I was hoping you'd fill us in on who it was loaned to and why
Was hoping for this too!
@@Willam_J It was astronomical!
William J, by now you’ve seen what RealSpaceModels did. You just have to learn to live with yourself.
Somebody who waited for a clear sky for 8 decades.
Speculum metal is a mixture of around two-thirds copper and one-third tin making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to optical devices until it was replaced by more modern materials such as metal-coated glass mirrors.
from Wikipedia.
Speculum literally means mirror in Latin too
Thank you. If I plot the Gaussian for comment usefulness, yours is on the right hand side of the bell curve.
Fascinating for an amateur optician and telescope maker, such as myself.
Possibly a Huygens eyepiece, the first compound type, invented in the 1660's, although usually the lens closer to the eye is smaller than the one closest to the mirror. Those speculum mirrors tarnished fairly quickly and re-polishing them also meant one had to simultaneously re-figure them to the correct curvature (as Rayleigh's Rule later showed, a spherical section is usable at f ratios of f8.2 or greater for a six inch mirror, as this example seems to be, and can be figured fairly easily when polishing with a pitch lap and optical rouge...for shorter focal ratios it has to be paraboloidal to eliminate spherical aberration...a far harder shape to figure and test for on larger mirrors, such as those used by Sir William and Caroline Herschel) - source: Jean Texereau's seminal work on amateur telescope making, "How to Make a Telescope", 1957. The book I followed to make my first Newtonian reflector back in 1966 when I was 14 years old.
Liked for the Harry Potter burn by Keith.
My only objection to that was Keith's description of them as children's books. I read them as an adult, suffering insomnia, waiting for my sick father to pass. But they are fantasy, with no connection to the real world.
@@UncleKennysPlace That was just an amusing little barb to characterize that master-student dynamic they use to explain things on camera. Don’t worry about it :)
I particularly liked how Brady invited it.
Curious as to exactly who had the the piece checked out for 80 odd years.
We really need Moore episodes of Objectivity with Keith!
Great to see this. This was very high end for its time and speculum mirrors got bigger and bigger, however, they were hard to fabricate and maintain and lost their reflectivity quite quickly; then in the 1850's someone invented silver on glass mirrors and that became the next big leap in telescope design. Glass is much easier to fabricate than speculum, the slivered coating stays shinny for much longer, and speculum became obsolete.
Brady's motions at 4:34 lol.
I like how in the drawing at 1:46 the mirror's curvature is super visible whereas in reality, the mirror looks basically flat.
I fully agree with Munjee Syed, please give a little more background information about objects like these.
At first the mirror does not look functional. But I could see Braidy's reflection on the selfie. That made me happy.😊😊😊
Keith "read another book" Moore
One can never read too many books.
I love how the history is still alive and healthy ❤️
Why, when looking at the accounts of using the telescope are portions exed/crossed out?
J H i don't know obviously but my guess would be simply spelling errors?
Backspace key broken
culwin yep 🤣
Wonderful! So Hadley’s telescope preceded William Herschel’s and must have served as a design model for Herschel to use when making his reflectors? Thanks for the video! More astro artifacts please!
Keith straight up told him to read another book lol
Keith and old boxes with astronomical equipment.
What could be better.
I'd love to know more about how the mirror was made, the curvature has to be extremely accurate I would think.
Keith is the sort of person who probably reads Being and Time by Heidegger at bedtime. Or Tractacus Logico-philosophicus.
@Jon Goat perhaps a bowlful of Cavendish gently burning away in the Peterson?
How would they polish the mirror to a nice sheen? What kind of metal is Speculum, Aluminum based or Silver or something else?
It's a copper/tin alloy.
Wonder when they decide that restoring the item (polishing in this case) is preferred to keeping it as is...?
It has more value as an artifact than as a working tool. So I doubt they will ever polish it (Unless someone pays them a wedge of cash I suppose)
Who could have borrowed an object for ~87 years, did the object remain in his/her possession until now. And did the Royal Society know where the object whereabouts in the past 87 years or did they thought it has gone missing 🤔
@MichaelKingsfordGray Just say museums.
Is “speculum” the material it’s made of?
"This happens March the second 1720 to 1721"
That's a very long March the second...
"I'm the man in the box
Buried in my sh
Won't you come and save me?
Save me"
I'd love to see this mirror polished and refitted into a tube for use again. It shouldn't be sitting around in the vaults!
Brady making a selfie with the mirror
Meanwhile the guy about to invent a device that reads the mirror's atoms and recreate the actual images of Saturn...
I'm sure the foam holding the lower doowackies dates from 1932.
Fascinating
What camera and lens was this shot with? Looks beautiful!
Funny how takes a "selfie" in a mirror that is from a time when we didn't even have photography for dozens of years to come.
Thank f**k it's Keith! Legend!
Pretty cool.
why not polish the mirror?
It will tarnish again quickly
Too much focal blur in this video, gave me a bit of eye-strain.
Just think that the lenses you put to your eye were used to gaze at Uranus 🤣
I wondered if John Hadley was the Hadley of Hadley Cells in meteorology. Apparently not - that was his brother George.
Hmmm... but if its a picture of your reflection pointing at itself, does that really count? :P
Numberphile! Terrance Tao Collatz Conjecture Update, PLEASE!
I watch a huge number of science/skeptic videos on RUclips, and yet RUclips has never "recommended" one of your videos to me.
I came here via Captain Disillusion on Twitter. Check your SEO?
(happy to be here, BTW)
3:34 children’s fiction? eXcUsE mE?
'tis true though
KEITH IS GOD ALL HAIL KEITH
I'd probably drop that the moment it was put in my hands from the weight of history... and also my clumsiness.
Isn't a speculum something the doctor sticks in your hoo-hah during an examination?
Yep. Speculum is also the name of the metal alloy that the mirror is made from 0:53. The name comes from the Latin 'speculum' meaning a mirror or reflector. I don't know if the medical instrument was at some time made from this metal or if the name perhaps comes from the Latin 'specere' meaning to look at or to view. I feel smarter for googling that ;)
🤔 Astronomy meets gynaecology