So many so little time ----
Obsolete biology theories
Lamarckism - but revitalised in Neo-Lamarckism - see also epigenetic inheritance
Maternal impression - obsoleted by genetic theory
Miasma theory of disease - obsoleted by germ theory of disease
Spontaneous generation (abiogenesis)
Recapitulation theory - or "ontogeny recapitulates phylogeny"
Obsolete chemistry theories
Caloric theory
Phlogiston theory - replaced by Lavoisier's work on oxidation
Obsolete physics theories
Aristotelian theory of gravity - discredited by Galileo
Aether - failed to be detected by the Michelson-Morley experiment, made obsolete by Einstein's work.
Caloric theory - Lavoisier's successor to phlogiston, obsolesced by Rumford's and Joule's work
Plum pudding model of the atom - assuming the protons and electrons were mixed together in a single mass
Emitter theory - another now-obsolete theory of light propagation.
Persistence of vision - to a fairly good level it is rejected by investigative psychologists
Obsolete astronomical and cosmological theories
Ptolemaic system/Geocentric universe - obsoleted by Copernicus and Galileo
Copernican system - obsoleted by Johannes Kepler and Isaac Newton
Obsolete geographical and climatological theories
Creationist theory - obsoleted by Big Bang theory and the theory of evolution.
Flat earth theory
The Open Polar Sea, an ice-free sea once supposed to surround the North Pole
Rain follows the plow - the theory that human settlement increases rainfall in arid regions
Obsolete medical theories
Theory of the four bodily humours
Eclecticism (medicine) - medical history - Some say it transformed into homeopathy and pseudoscience.
Obsolete branches of enquiry
Alchemy, which led to the development of chemistry
Astrology, which led to the development of astronomy
Phrenology, was once widely studied but now considered a pseudoscience
Numerology, as distinct from number theory, now considered a pseudoscience
Approximate theories
Here are theories that are no longer considered the most complete representation of reality, but are still useful in particular domains. For many theories a more complete model is known, but in practical use the coarser approximation provides good results with much less calculation.
Steady State - The Big Bang and dark matter threaten to destroy this comfortable world picture.
Universe - The possibility of Multiverses is one of the consequences of cosmic inflation.
Atoms are no longer thought to be indivisible, but are now seen to be composites.
Nuclei disintegrate at high energy.
Heliocentric universe theory - This is still used in the coordinate system of celestial mechanics.
Newtonian mechanics - obsoleted by Theory of Relativity and quantum mechanics. Still useful in engineering and physics at either middling (human) scales or where appreciable fractions of the speed of light need not be considered.
Bohr model of the atom - Allows for exact solution of the hydrogen atom, but larger atoms are not well described.
Newton's sine-square law for the force of a fluid on a body - no longer considered useful at low speeds, though it has found application in hypersonic flow
Theories whose significance was overstated
Land bridges - Though temporary connections between land masses sometimes allowed migrations (as when sea levels were lowered during ice ages), the actual splitting of continents by plate tectonics has been more important.
Do it like so:
[a href="?"][b][big]XXX[/big][/b][/a]
Replace the "[" brackets with "<" and the "]" brackets with ">"
The ? gets replaced by the site's url. The XXX is replaced by the title of the link that will show up in the thread. Nothing to it.
(Information supplied generously by PatrickHenry,
Slightly modified by me)