The geometry of it all

Is it true you have to read a sundial at night with a flashlight?

In Dodge City, Kansas, not far from where Matt and Kitty spent all their time, you may still be able to find two large sundials at the old railroad station.?ÿ I remember seeing them about 60 years ago and was amazed.?ÿ Side by side, they showed different times.?ÿ In those days the time line between Central Time and Mountain Time ran through Dodge City (or nearby anyway).?ÿ Travelers going west needed to adjust their watches to match the western sundial and those going east needed to adjust their watches to match the eastern sundial.?ÿ Could not wrap my little mind around the fact that the shadows from the two tall poles hit different numbers.

https://www.roadsideamerica.com/tip/24644#:~:text=Dodge%20City%2C%20Kansas%3A%20Time%20Zone,station%2C%20end%20of%20the%20platform.&text=Directions%3A,Earp%20Blvd%20between%20Central%20Ave.

There is a really cool example of Foucault's pendulum clock in the science museum in London. A simple no tech way to tell the time.

I believe similar examples can be found around the world, Paris for example and one in the Franklin Institute.

Never heard of Foucault's Pendulum? Here's a wee explainer

@jimcox?ÿ

I did enjoy the novel, a bit paranoid maybe, but a good read.

Posted by: @dave-lindell

Is it true you have to read a sundial at night with a flashlight?

Of course! What time do you want it to be?

Many years ago I overheard a fellow in a bar showing off his new watch that would light up in the dark so he could see what time it was.?ÿ It said it really came in handy when he was between the sheets because he would know whether or not it was time to go home to his wife.

@holy-cow?ÿ

Must have used one of these:?ÿ

?ÿ

@holy-cow?ÿ ?ÿyou can see them on Google earth... not the dog though.

@mightymoe They want you to think it's just paranoia?ÿ

Welcome, friend.

Some dials can be used at night for taking the azimuth of celestial bodies and you need a flashlight indeed to read the?ÿdial. Look up the Abrams SC-1 used during WWII.

@holy-cow?ÿ

Both poles had parallel shadows pointing at the same solar time, but you can write any number you want on the dial. Before the telegraph became available in most stations the railroads were using sundials and pocket watches for synchronizing the trains. In France sundials were used until 1900 and some dials can be seen even today in older stations. After a bad train wreck due to a pocket watch having stopped for a few minutes after a fall, it was decided to issue "railroad watches" to employees. These watches were certified and the watchmakers had marine chronometers in the shop to set the time. The marine chronometers were periodically set from telegraph stations.?ÿ In England, before the telegraph,?ÿ a fancy sundial called a "dipleidoscope" was invented, which allowed people to set their pocket watches at home with an accuracy of seconds. The instrument maker who made them was John Dent of Big Ben fame.

They used to have a large Foucault pendulum at the Smithsonian in Washington DC,?ÿ as it swung it would knock down pins one by one.

@gordon-svedberg?ÿ

I remembered seeing one like that when I was a kid.

Thanks for reminding me where it was.

We were only in DC for a few days, but did visit the Smithsonian - it obviously made an impression

@james-fleming

I knew it, I always knew,,,,,,,,you're one of them!!!!!

Need to check N-S alignment, but....

@erwin-wechsler?ÿ

These were big enough that to an eight year-old kid it was a good trip from seeing noon on one and 11:00 on the other.?ÿ You needed to be more or less directly in front of the shadow to read the big concrete number.

This is a pretty cool mashup of maths and design.
https://www.thingiverse.com/thing:1068443

@martin_au

Yes, I bought one on eBay as soon as they came out. It shows time in 20 minute increments. It is made by 3D printing and they come from the former Yugoslavia. Smart fellow the designer!