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Bluelighter
When the senses fail, your intuition takes over; that's how scientists start there work trying to understand the mysteries of life. They sense something first, then go out and prove it (or try to).
Well no, actually, that's not at all how the scientific method works, nor, to my knowledge, is such a description reflective of how the discipline is/has been conducted by real scientists in this or any time period. Scientists do not formulate and test their hypotheses according to the whimsical caprice of their 'intuitions.' With their well-trained eyes and brains, they detect meaningful patterns in the natural world which can be assessed for descriptive and/or predictive validity by way of rigorous experimentation and applied mathematics. If it weren't for the coldly analytical Newton and the preternaturally sagacious Galileo, neither you nor I would 'know' the first thing about gravity. Without the ingenuity of a Gauss or Maxwell, you would be similarly ignorant of the force of electromagnetism. It is not the 'intuition' and 'feelings' of these great minds that we must predominately thank for their illuminating theories, but, rather, their singular, almost superhuman powers of problem-solving ingenuity and logical thought.
Come to think of it, it's interesting that you chose these examples in particular, since they prove so fruitful in explaining the power of the power of the scientific method in comparison, to, say, shamanism. The chief reason that anyone 'knows that gravity is there' is that, in fact, you really can see it, hence the possibility of Newton's formalizations in the first place. Insofar as gravity describes a fundamental force of nature, one can perceive it in action anytime one drops something, attempts to float for any longer than half a second in midair, etc. The converse is true with electromagnetism, but in this case, one can sometimes literally see its most direct manifestations, e.g., an arc of lightning.