I want to test electromagnetism. The first idea I came up with was to use an ammeter and voltmeter for circuitry.
However, these instruments were designed based on electromagnetism. So I think this experiment would involve circular reasoning and be invalid.
How can I verify electromagnetism?
If you are not content with the experiments using ammeter and voltmeter, you can try the following simple experiments.
To demonstrate that dynamic magnetic field can create electrical current, use the dynamo-electrical generator setup as in the following figure (the figure is from this site).
To demonstrate that an electric current creates a magnetic field, try the experiment set up as in the following figure. Passing a direct electrical current through a loop of green wire will create a magnetic field around the wire. The compasses will be deflected when the electrical current runs through the loop of green wire.
The details of the experiment can be found at Circles of Magnetism
It should be noted that the ammeter and the voltmeter are created from the well-known, established principles learned from these earlier, simpler experiments. They (the ammeter and the voltmeter) just come in a handy, easy to use, and easy to read form. Using them in experiments does not mean the involved experiments use circular reasoning and are invalid.
Science does not really care about circular reasoning:
Why is scientism philosophically wrong?
Is there an alternative to the scientific method?
What basis do we have for certainty in current scientific theories?
In fact our units of measurement have gone from direct comparison with for instance "the royal yardstick", to increasingly being defined in terms of one another:
That said, in your practical application you can use ammeter and voltmeter as quantifiers for an external metric, like the force exerted by the eletromagnet, thereby building a relationship between Volt, Amps, Newtons and distance.
I simply love the story of Hertz's verification of Maxwell's equations because it contains the most awesome faulty prediction about the future ever:
Hertz did not realize the practical importance of his radio wave experiments. He stated that:
"It's of no use whatsoever[...] this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."
Asked about the applications of his discoveries, Hertz replied:
"Nothing, I guess."
He had just discovered radio.
Anyway... Hertz's experimental setup was as follows:
It is described in further details here.
1) 'Electromagnetism' is not a question or a fact, it is a collection of theories. You need a more specific question before you can test it.
2) You can only test it, you cannot verify it. If science were 'verified' and actually true it would stop changing, which would be the death of the entire endeavor.
Karl Popper's demarcation criterion, and the way it fits together with scientific practice makes this point very clearly. A theory is valuable to the degree it risks being falsified by future data. And progress is the falisification of one theory in favor of its competitors. Something is 'verified' only to the degree that the other theories it relies upon have faced such risks and survived them.
3) You can never completely escape this problem of relying upon related technologies to test your theories. All theories are circularly constructed. Theories both determine what counts as an observation, and at the same time rely upon observations to evaluate their contents. The closest you can come is for all your theories to back each other up and share a philosophical basis, resulting in a 'paradigm'.
Thomas Kuhn's view of the history of science shows how scientific tradition all fits together and constitutes progress, even though there is no starting point or absolute basis.
4) Outside of some kind of overarching paradigm, you can't even test the theory with any certainty. You can check that it predicts what happens, but that does not make it a valid explanation, only a predictive mechanism. It could be right for the wrong reasons. Only with a context that is so complete that it has something to say about a large segment of nature can you claim that predictions result in explanations. And predictions are all that theories actually provide.
The 'story' part of Feyerabend's book 'Against Method' gives a very good interpretation of why Galileo could not convince his contemporaries of the unity of laws on Earth and in Space. Without a unified framework made up of a large number of interlocking pieces, no part of the notion could be proven better than the existing explanations.
