It's just a fancy light switch for a 90 odd year old carriage, it lets you have full or half lighting from the batteries. I will have to snap a shot of one in-situ next time I'm near one.

This one just shouts "mad", sans "scientist".

Most people rent it for the occasion, but I was fortunate enough to find one in my grandfather's cupboard that fit like a glove. It was probably made in the early 1930s, and still had its matching cufflinks in a pocket.

The cufflinks were made out of mother-of-pearl and bakelite!

On a related subject: I just read J.E Gordon's New Science of Strong Materials, where he claims that 'it's being said that the first commercial application of Bakelite was for the gear-knob of Rolls-Royce'. Do you know if that's true?

Here is another way to show such an arrangement. I have seen it used for Local/Remote/Stop selector switches for switchgear (control circuitry that eventually uses a relay to keep the human's hand away from those nasty voltages)

http://commons.wikimedia.org/wiki/File:Dans_knife_switch_v2alt.PNG

One of the motorcycles I own was built in the Socialist Worker's Paradise that was the German Democratic Republic, by the Motorradwerke Zschopau, MZ for short, in 1981. And of course, like the Trabant and the Praktica, it looked 20 years older than it actually was, with technology to match. Which is not to say that it didn't work fine, but the 6V electric systems the MZ engineers had bestowed on it was somewhat lacking, and consequently riding at night on unlit and otherwise deserted roads a little more exciting than one would like.

So I ordered a 12V conversion kit. To be mounted in place of the original generator.

A motorcycle's generator is often mounted on one end of the crankshaft, and when it is, it's often enclosed in the crankcase. This machine being a two-stroke it doesn't have oil present there, and when I opened up the generator compartment a most concentrated bakelite odour wafted out. Did I mention that the crankcase gets hot? That was twenty years of bakelite gassing out its volatile components into a sealed compartment.

So the diagram does get a bit bigger. Maybe something like http://commons.wikimedia.org/wiki/File:Dans_knife_switch_v2.svg

You are so lucky!

I know!

(Anne totally does not get this. I'll make sure she reads this, to see all us dorks cooing over this thing like 1950s housewives at a Tupperware party.)

I passed up (or didn't bid enough to buy) several other switches before I finally found this one. The basic antenna-isolator type of knife switch comes up quite often on eBay, and sometimes there are monstrous old things with porcelain handles and no baseplate, because they used to be anchor-bolted to a concrete wall.

My only question is: Does it still smell like it should?

It pretty much just smells of kerosene at the moment, because I spritzed it with WD-40 to loosen the crud of decades and get the terminal screws moving again. Now everything moves freely and makes proper contact, and it's also now possible to handle the thing without having to wash your hands afterwards.

I was pleased, however, to be able to apply the smell-your-thumb test to the base to verify that it was Bakelite.

That test goes like this:

1: Vigorously rub some part of the object you think might be Bakelite with the pad of your thumb. You want enough friction that your thumb becomes uncomfortably warm.

2: Quickly smell your thumb.

If, for a second or two, there's a distinct smell of phenolic resin - which is kind of hard to describe, but because phenolic is still used for circuit boards anybody who's encountered some hot electronics will know it - then the object is Bakelite.

This test is a good one because it doesn't harm the thing you're testing - well, not unless it's some fragile little hair clip or something, and you rub so hard that you snap it.

(There are a variety of other Bakelite tests, the dumbest of which is the "red-hot needle" one, in which you actually burn a little hole in the item you're testing. To be fair, that test will probably also tell you if the item is made of celluloid instead of Bakelite, because the needle will then probably set it on fire. Celluloid
burns real good.)