Hacker News Reader

Comment by intrasight | Hacker News Reader

Am curious. How, with 17th century technology, could you have a geometry where I can see you but you can't see me? Glass treatment? Narrow viewing port?

View on HN

Don't need any special tech or geometry, just light. If it's relatively darker in the watched-from areas it's harder to see in than out.

Light and perhaps curtains in the central area would probably do the trick.

"By Blinds, and other contrivances, the Inspectors concealed from the observation of the Prisoners: hence the sentiment of a sort of invisible omnipresence."

— Jeremy Bentham (1791). Panopticon, or The Inspection House

Something like "one way mirrors" should work.

They're really just glass with a partially reflective layer.

When one side is brightly lit and the other side isn't you get the desired effect.

If the internet is to be believed they did not have one way mirrors in the 17th century. They were invented in the early 1900s.

However, looking at the patent for what is supposed to be the first it says that there were earlier attempts--they just sucked because making the partially reflective layer was difficult and expensive and not durable enough when used on outdoor advertising devices.

Yes, you read that right. Advertising. Technology being driven by someone's desire to show ads is not new.

The thing the inventor was building was a case for displaying advertising posters. The case had a glass front, and the poster was behind the glass, with powerful lights behind the poster. When the lights were off the glass would appear to people looking at the case to be a mirror. When the lights were on the poster could be seen.

Plain glass works fine for this, but they were perfectly capable of making one way mirrors at the time. The historical term is "half silvered mirror", which were used in a lot of early scientific research in optics.

Frankly you could just use blinds though.

If the internet is to be believed silvered mirrors also came after the 17th century. Wikipedia has silvered mirrors as being from 1835.

Silvering is a separate and older process than silver mirrors, as in the metal silver applied to a glass surface.

The Wikipedia page on silvering points to the 1400s in Europe, and the 10th century for the eastern Mediterranean : https://en.wikipedia.org/wiki/Silvering

a circular room looking out from a high point facing an exterior round wall of cells that look in

Something like a pinhole camera. If you have a piece of card with a pinprick hole in it, you can look through that hole and see a wide view, but a person in front of you wouldn't be able to see much of you through that same hole.

Prisons in the 1800s were dark

It's a metaphor mostly.

Reply on news.ycombinator.com