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 :)
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.
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.
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 🤔
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!
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 RU-vid, and yet RU-vid 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 ;)
