An example of an analogy used to explain a scientific phenomenon:
"Someone else believes that there can be particles with the property of levity as well as gravity and that the matter of the [comet] tails levitates and trough its levitation ascends away from the sun. But…I suspect that that this ascent arises rather from the rarefaction of the matter of the tails. Smoke ascends in a chimney by the impulses of the air in which it floats. This air rarefied by heat, ascends because of its diminished specific gravity and carries along with it the entangled smoke. Why should the tail of a comet not ascend away from the sun in the same manner?"
Isaac Newton (1999) Mathematical Principles of Natural Philosophy (3rd edition, 1726): The authoritative translation (I. Bernard Cohen and Anne Whitman), University of California Press
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The idea (that Newton ascribes to an unnamed other) that some materials might exert a property of levity (a tendency to ascend), as an inherent quality distinct from gravity, was once quite common.
