PSU Voltage Surges

Yes, that was my Feynman reference. I thought it was in "Genius" but I guess it's in Surely You Are Joking.

He was a good circuit designer as well as a serious physicist. That's an unusual combination.

John Larkin Highland Tech Glen Canyon Design Center Lunatic Fringe Electronics

I haven't used a mercury relay for many years but I did have to repair a mercury tilt switch last year.

It was part of the contol system for the water supply in a house that used pumped water from a well. The switch was mounted on a wooden plank that spanned across the top of the water tank in the attic, operated by a see-saw arrangement with a large cork float hanging by a chain on one side and a balance weight hanging on the other side. It controlled the fairly substantial motor of a pump that drew water from the well some distance away and delivered it to the tank.

It had stopped working after a builder went up in the attic several months previously, so the owner had returned the system to manual control. When I investigated, I found the entire assembly in the bottom of the tank, under water and still connected to the 240v mains supply. It appears the builder had carelessly knocked it in but (sensibly) decided not to try to retieve it from the water.

It was a horrible mess and I had to machine up new brass terminals, make flexible braids and replace the over-centre springs. I fixed the plank so it couldn't fall in again. The switch has worked now for over a year and I expect it will outlive me and it's owner (...and the builder!)

I bought a ton of old electronic surplus from some deceased ham's estate and discovered a bunch of old mercury tilt switches among the 'treasures' after they'd been delivered. I know when they would have been made, but clearly it was a *long* time ago. There must have been half an ounce of mercury metal in each switch easily! In bygone times, everything was over-engineered it seems. Fabulous quality as well.

Mercury-wetted reed switches aren't big, and they weren't particularly expensive when I was using them. Regular dry reed switches are good for about 10 million contact closures, and mercury-wetted reeds are good for

That's not what we were talking about.

Pickering used to be a reliable source of mercury wetted reed relays but now they only cater to the legacy market. Health and safety is now nervous about mercury, even the tiny amount encapsulated in a glass reed capsule.

The mercury can only get out if the capsule is smashed, so they aren't toxic.

By which he means that he responds well to flattery, but regards anybody who doesn't flatter him as a creep.

There you have it - he has an insatiable addiction to flattery, which he ought to be apologetic about, but no grasp of how this looks to the rest of the world.

I mostly take about an hour or two. I needed four books for an intercontinental flight. The introduction of the Kindle made long flights appreciably easier.

That's one way of looking at it.

My wife was just as bad. when we sold our big house in Nijmegen, I sold off most of my English language science fiction collection to the local used book chain, for about a thousand euros - about 0.20 euro per book.

But had no idea how. It was suck it and see diagnosis, which happened to turn out right. No one argues with the fact that Feynman was clever, but he did know a lot more about physics than electronics.

Serious physicists are usually a lot better at physics than circuit design. The Review of Scientific Instruments makes this obvious on a regular basis. Feynman doesn't seem to have been famous for his circuit design skills. You have to master a great deal of information to be good at circuit design, and a whole lot more to be good at physics. There have been people who have done both, but they are rare.

That may be perfectly true, but lawyers can be very toxic...bad for your health & wealth!

They were used in situations where the utmost reliability was essential and for controlling heavy surge or inductive loads. Capacitors were very expensive and unreliable in those days, so switches didn't normally have suppressors.

Mercury vapour is very easily detectable by atomic fluorescence. You can use a mercury lamp in a silica bulb to generate lots of the mercury resonance line at 253.7nm.

Suck the air that is supposed to be contaminated with mercury vapour through a tube, shine the mercury resonance line down the tube, and any mercury vapour there will absorb the photons briefly, and re-radiate them in random directions, where a detector at the side of the tube can be set up to detect only the fluorescence.

It's very sensitive, very specific and can be very accurate.

If there's no detectable mercury around the lawyers can be sent packing.

When I was a graduate student in chemistry we used a lot of mercury, and the labs got checked regularly. The only place that tested positive for mercury vapour was the small lab that was used clean up used mercury by distillation, and that still pretty safe. Mercury spills were dusted with flowers of sulphur, which did seem to soak up the vapour.

Alfred Stock's book on mercury vacuum lines (from 1927) was a bit terrifying - he managed to get mercury poisoning early in his a career and did warn against it.