Fun. It reminded me of the https://en.wikipedia.org/wiki/Clock_of_the_Long_Now, which uses a similar noon-sun mechanism for keeping the daily clock cycle accurate.
So it's still local noon.
I’m joking but this is also a real thing. For an example, see this code in the astrolib port used by SensorWatch’s “movement” project:
https://github.com/joeycastillo/Sensor-Watch/blob/e8f31beb70...
https://en.wikipedia.org/wiki/Analemma
So the mechanism of a uniaxial gimbal (as pictured in the examples at end of article, and presumably manually adjusted) holding the magnifying glass would seem to introduce some error over the course of a year. But I like the concept, having some weird affinity for automation based on low-tech / earlier-tech principles.
Wouldn't this setup actually work though? At least if it's a proper sundial cannon.
Most components of that system are mechanical clocks, which do keep the time on their own, they just drift. The only exception is the gunner who fully relies on an external time signal.
So if that were all, the system would work for a while, but slowly drift and become ever more inaccurate, until it basically has nothing do do with the actual time anymore.
However, the gunner does not always operate the cannon: He only does on cloudy days. On sunny days, the cannon operates itself, using the time signal of the actual sun - which is then passed through the chain and let's the mechanical clocks resync to "sun time".
So in effect, the system's time signal comes from the sun. The rest is just an overly complicated way to "interpolate" the time if the sun is not visible or not at noon.
(Now I also wonder if someone ever build a "self-syncing" mechanical clock - e.g. for a clocktower - using this principle: Use a standard clockwork, but add some mechanism that resets the clock to noon when a focused beam of sunlight hits a certain point.)
Only when used in conjunction with a standardised 'mean-time' 24 hour clock. If you plot the position of the sun at the same mean clock time, then sometimes the sun will be ahead, sometimes behind.
> However, the gunner does not always operate the cannon: He only does on cloudy days. On sunny days, the cannon operates itself, using the time signal of the actual sun
That's why I don't understand how you came to this conclusion, what's your thinking behind it?
> The 6-pound cannon is fired everyday at 1 PM, from May to September. On sunny days the sun automatically sets it to light, but on days when clouds obscure the sun, the sun gunner on duty fires the midday salute with a match.
I imagine that was what reminded the GP of the joke and I kinda used it as context - but yeah, on rereading, it's not part of the joke. I admit, I jumped to conclusions there.
The recoil both gives you kinetic energy and an impulse that is timed at noon. You could use it to drive some mechanism that prepares the cannon for the next day, e.g. refills gunpowder and adjusts the magnifying glass.
The latter could be done by having a gear with a cam that is driven 1/365 forward with each firing of the cannon and that encodes the position of the magnifying glass for each day of the year.
That only leaves you to design the exact shape of the cam. And deal with cloudy days and leap years...