Full size model of some experimental apparatus

My daughter is doing a PhD which includes investigations of the original experiments of someone famous, see if you can work out who.

The only information left from the experiments are the original results, sketches and notes on the apparatus. This is my reproduction based on the notes and the sketches shown below.

Martin C

Edited By Martin Connelly on 10/01/2022 14:36:53

Facetious;
Expansion coefficient of frog legs during broiling originally postulated by Madam Rana Shrincage

pgk

Seebeck? Thermocouples, boiling water in the vessel with the burner, Ice in the other and a galvanometer to measure the voltage. Not sure what the two little white pots are for

Edited By duncan webster on 10/01/2022 15:07:45

Greetings Martin, was that a Michael Faraday experiment?

Regards

Brian B

Seebeck Effect?

Battery?

Ches

The two little cups are for mercury, there were no standards for electrical equipment or common methods of making a good contact. Copper wire was dipped in the mercury to complete a circuit for the experiment. The copper pots are for iced water and boiling water, the silvery bar is bismuth for thermocouple effect but no bullseyes yet.

Martin C

Hmm...the needle (with metal end?) suspended by the thread must be registering some kind of electromagnetic force? I'm not not sure who the inventor is.

Ches

The needle is a magnet.

Martin C

Would Fleming (of the Left Hand Rule fame) have anything to do with it?

Rob

No, not Fleming. It is from around the same time as Fleming and Faraday who followed on from others such as Coulomb and Oersted. To some extent it was based on the apparatus Coulomb used for his investigations into static electricity.

Martin C

I suggested Seebeck because he discovered the Thermocouple effect.

The apparatus pictured by Martin has hot and cold junctions between copper strip and another metal, probably iron. The cold end copper strip passes under a suspended magnetic compass needle. The needle will deflect whenever current flows around the circuit, and the eye-piece/microscope allows tiny movements to be seen. The needle is a simple galvanometer and I'm pretty sure measuring the angle allows the EMF to be deduced (voltage). I remember because I made a complete mess of the calculations at school during a physics practical and was humiliated in front of the whole class.

Not sure about the mercury pots: are they just a low resistance switch? I guess the apparatus is brought up to temperature, the needle is zeroed, and then the circuit made by adding mercury. At that point the temperature differences are stable and the deflection is noted.

Peltier Effect is the thermocouple in reverse. Applying a voltage causes one side of the thermocouple to cool down.

Lord Kelvin (William Thompson), brought the understanding of Peltier and Seebeck effects together. Possibly the apparatus is his, but I would have expected a better galvanometer.

Dave

Something with Peltier effect?

Too late!

Resistance? Georg Ohm?

Dave you've got the process down pat, the metals in the thermocouple are copper and bismuth. The magnet is aligned along the magnetic north-south when at rest over the zero on the scale (the whole apparatus has to be aligned to do this). When the circuit is made a current flows and the needle is deflected by the resultant magnetic field. The top is then rotated to bring the needle back to zero and the rotation measured against the upper scale indicated the current that deflected the needle.

The thermocouple was used as batteries of the time were not able to give a consistently even voltage and current for the fine measurements needed.

So what happens when different lengths of wire or different thicknesses of wire are used to complete the circuit? That should give away the law named after the original experimenter.

Martin C

Andrew D got there when I was posting. It was Georg Ohm's experiment that he used to derive Ohm's law in 1826.

He was not a trained scientist and kept poor notes. On top of that the original equipment is lost. The PhD is investigating how he used the apparatus, how hard it was to get repeatable results and if the maths he used can result in Ohm's Law as he seemed to make a few leaps in the numbers. Then there is the process he went through to come up with the apparatus as it was not the first he used, he had tried batteries and just one thermocouple before and the apparatus possibly used some parts of previous pieces from those experiments. 

Martin C

Edited By Martin Connelly on 10/01/2022 16:41:58

Martin,

Here's a good video on Mr Ohm and how he struggled to get his discovery recognised ....

Ohm's Law: History and Biography - https://www.youtube.com/watch?v=fk_BpXlfZ8U

As a retired Mech Eng I did do some college courses on electronics/electrical but we never got to really know the background on how theories/laws became accepted. I'm sure you and your daughter will be aware of all this but for folks like myself it was a very interesting 18 mins viewing.

Regards,

Ches

I have seen that video recently as you suspected. I don't know if my daughter has seen it, she is trying to rely on original sources of data and has even gone so far as to translating the German texts herself to avoid any issues with interpretation of what was written.

Ohm was using lines as a unit of measurement, there were a certain number of lines to an inch but I had to point out to her that she then needed to know what inch he was using in 1826 Germany (which wasn't Germany at the time). It's been an interesting process assisting in this task. I have been helping her with the whys and hows of the manufacturing process, and what was possible then compared with what is possible now, so that it may be possible for the reasons for how the design was the way it was may be explained.

One thing we have not been able to get hold of is gold lahn, used to suspend the magnet. There are plenty of people selling gold lahn on the internet but nowadays it is all plastic covered aluminium and real genuine 24 carat gold lahn seems to be unavailable. We have had to replace the fine ribbon of gold he used with a braided polyester ribbon as even the fine hairsprings used in watches have too much torsional resistance to overcome.

Martin C

Martin,

Yes, I imagine it has been very interesting helping your daughter. She is absolutely right in using original sources.

The '1826 German Inch'...I'll need to do a bit of digging on that one myself out of curiosity...again, sounds interesting.

I did wonder about the thread holding the needle and how it would need to be 'torqueless'.

Ches