Dear Heinz
Thanks for your comments. Despite your explanation I still don't see any justification of your claim that those theories came out of the blue. For instance, Newton was aware that gravitation was not conveyed in total emptiness, he always held that there was aether. However, his theory does not include it and for this he was criticized. So why at the end was his theory established? First because it made testable predictions and explained known phenomena. Besides, at that time people discovered that it was possible to create vacuum with machines and that light and gravitation could travel through the vacuum. This was an argument that many invoke to justify Newton's gravitational theory. When one studies relativity one easily realizes from analyzing Newton's theory that this formulation suggests that gravitation and acceleration are strongly related: [math]F=ma=G\frac{mM}{r^2}[/math]
by eliminating the inertial mass
[math]a=g=G\frac{M}{r^2}[/math]
we see arrive at the Galilean equivalence principle(Einstein's happiest thought). The rest was just to put these ideas in mathematical terms following the four dimensional formulation of special relativity derived by Minkowski. So, I see no "out of the blue" and similarly for the theory of electrodynamics. For this was also a long and complex process that one can trace back. I do agree that some ideas may come out of the blue, but as you put say it they came from some pre-knowledge.
As for your comments on philosophy, I am aware of Popper, I have read his most important works on the philosophy of science. I have not read much about Spinoza. I know that sometimes propositions cannot be tested for they seem to be beyond experience or data, but as I said, data requires a theoretical framework to have meaning. Experimentation itself cannot rule out propositions because data itself depends on the theoretical framework where laws (principles, propositions) and definitions are embedded. So, in my opinion a model, understood as an abstract construction of some phenomenon, can be useful to understand something about reality (this is how we have built it). For instance, I suppose that materials are composed of atoms with a given arrangement. The atomic composition and the arrangement of the atoms define the physical properties of the material. If I check such or such property of that material and fits with my predictions it means that my model is correct and therefore my model does have explanatory powers because it is helping to understand the observed phenomenon. Models along with the principles help us understand reality.
Israel