What is this #2: Answer

Reader Fruity was the first to correctly name this device - on just the 9th comment. Impressive. Honestly, when I found this thing I had no clue. I asked other physicists and none of us were sure. However, I did find the answer. Let me show you my secret.


I don't know how old this thing is, but it is old. When I open it, my nose and eyes get all tingly - probably from the mold. Here is that apparatus in the book (tome):


I can't show you the whole page because it has other stuff of awesomeness that I want to show you later. But, I can show you the description for that item.


I am still giving Fruity the credit for the answer "Ampere's Rule Apparatus", but clearly The Tome of Knowing says "Mounted Conductor (Ampere's Law Stand)". Basically, you run some current through this thing and you can place a magnetic compass at different locations to see the deflections. Here, I made a quick video of it.

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"I am still giving Fruity the credit for the answer "Ampere's Rule Apparatus", but clearly The Tome of Knowing says "Mounted Conductor (Ampere's Law Stand)"."

Too funny.

Can't remember the exact words I googled, vintage, Welch, physics and apparatus come to mind. This link popped up and voila!

Out of curiosity, when was that Cenco sales catalog published?

By Fruity (Aimee) (not verified) on 31 Aug 2010 #permalink


I don't have a publish date - let's just say old. Actually, I didn't look too hard for the date - maybe it already molded away.

I not trying to be snarky here: it was really nice to see you have the confidence to show a blown demo, and how calmly you dealt with it.

I forget what settings I use for a similar demo, but it is quite a bit more than 2 A. The wire used can take a lot. It helps to get the vector sum of the earth's field and the wire's field looking more like what you expect if the earth wasn't there.


1) I welcome and encourage all forms of snarkiness. How can I be snarky and not expect to get some back? Bring it on.

2) That power supply only went up to around 2 amps.

3) I really should have just restarted the whole video, but I was lazy.

Good way to blow up your laboratory power supply, especially those with poor or no current limiting. I am guessing that the resistance of the apparatus is very low and will appear as a short to the power supply. You may want to put a 10 ohm resistor in series to give the supply a easier load to drive. Make sure it has a high enough dissipation rating and be careful of the heat it will generate. If you don't have a suitable resistor, a light bulb in series will work as well. Just remember to take your voltage measurements for any calculations across the apparatus and not the power supply.

By Bill Curry (not verified) on 02 Sep 2010 #permalink