Chronograph

About the Chronograph

Transcript from tour of the observatory with XXX (2021)

So the chronograph - and he had one here --that was made here, from the designs of William Bond-- Chronograph is a horizontal brass drum, with paper wound around it. And there's a clock drive? mechanism which we call a conical/mechanical? pendulum that there be a heavyweight that would pull on a chain and a series of gears designed to rotate this drum once around every say two minutes, and there be a pen and the pen would be on a little carriage that had a spiral on it, so as time moves along a gear turns the pen and moves it, say, from left to right. So if you did nothing didn't touch anything depend would trace a spiral like this around on the paper.

But if you had a push button --an electric push button on cord-- you would hit that button and a magnet, an electromagnet on the pen would cause it to jump like this! so when it jumps left and right you would say OK first I'm going to record that it's me and you had a special code for you (versus another observer) like I'm 3 blips on a space in another blip or something; and then you do a series of blips saying we're about to do this star --Star #5 or something-- and then you'd wait and when you see the star crossing wire #1 you did a button and it will cause a blip and So what the tracings look like is you unroll you take the paper off and you put it on the table, and you'll see align like this and then you'll see a little square blip coming up, and another one each time you press the button you take a ruler and you put it across them and you measure how far it was from the beginning of each minute. So in the meantime, you took your clock --not the bond one but one of the Molineux or other wall clocks-- and you had electric wires going to it, two of them, and so when the pendulum would swing, the pendulum had a little bucket of mercury and a little pin that would sweep through the bucket of mercury and close a circuit. So the clock itself is pushing a button every second. He's got to measure the except for the first second of each minute so you could tell when the minutes started, so it would do 59 of these little dots so you can put your ruler on and say: Oh here's the beginning of this minute, and here's how far away the clock the first wire was -- we also call them wires or spider-wires was because they were made of spider threads. Because - Noooo! Yeah I guess because spider thread threads was the finest thing that you could get - It was the finest thing you could get. Oh my god You would illuminate them from the side with a tiny little gas lamp and spider threads are very - there was a fellow selling a supply of spider web material on eBay recently, yeah from the 1950s Why didn't you get it? In modern days, in the 1940s, in the about the 1940s, we went to verifying tungsten wires and spiders weren't used anymore... but observatories kept a spider, he probably had his spider or he got him from someone who supplied spider web material. Cos it's so immensely strong but so very very thin if it's too thick it blocks too much of the star and you can't tell the star's centre as it's hidden.