1. Imponderable fluids and the Laplacian synthesis
1. Traité de mécanique céleste (1805).
1. A Newtonian approach--Laplace concerned with forces between particles and forces within fluids.
2. Heat, light, electricity, magnetism, each treated as a separate subtle fluid.
3. Laplaces synthesis is a synthesis in mathematical terms only (that is, for Laplace, electricity and magnetism were entirely separate phenomena).
2. Interrelationships between phenomena:
1. metals + chemicals electricity (Volta, 1800. Ex: a battery).
2. electricity heat (Ex: a heating coil like the one on your stove).
3. electricity light (Ex: a heating coil or a light bulb).
4. electricity magnetism (Oersted, 1820s. Ex: a compass needle will point toward a wire carrying electric current).
5. magnetism + motion electric current (Faraday, 1830s. Ex: an electric generator).
6. electricity + magnetism motion (Faraday, 1830s. Ex: an electric motor).
3. Rethinking the nature of light
1. Youngs double slit experiment convinces most physicists that light is a wave, not a particle as Newton suggested.
2. It was well known that the properties of a wave are dictated by the medium that carries the wave. Ether was proposed as the hypothetical medium that carries light waves.
3. People started investigating optical phenomena in the hopes of learning more about the ether.
4. Faraday and the shift from forces to fields
1. Faraday was working on electricity and magnetism as though each was the effect of forces within separate ethers.
1. Mathematically, it made sense to think about all of the forces exerted on a body in terms of the overall affect the combined forces have.
2. He referred to this overall affect as a field.
2. Thinking in terms of a field allowed Faraday to propose different results for motion perpendicular to a field than motion parallel to a field.
3. The interrelations between phenomena led Faraday to wonder about possible interrelations between the fields.
5. James Clerk Maxwell and the Maxwellian Synthesis
1. On Faradays Lines of Force, (1856).
1. A geometrical model for Faraday’s lines of force.
2. Maxwell asked his readers to imagine the lines of force to be like tubes full of incompressible fluid.
3. He then derived equations to describe the strength of the magnetic field at various points around a magnet.
2. On physical lines of force, (1861).
1. A mechanical model (cf. Nye, page 75).
2. Each hexagon is a portion of ether.
1. Rotation of vortices = magnetic field
2. Idler Wheels prevent the ether vortices from cancelling each other out.
3. Translation of idler wheels = electric current
4. Vibration of ether = light
3. So electric current (translation of idler wheels) produces a magnetic field and magnetic fields produce spinning of idler wheels (which can be seen as electric current if a wire is placed so that the wheels can translate).
4. Note that Maxwell has combined in one mechanical model electricity, magnetism, and light.
3. Experimental verification
1. Maxwell’s theory suggests that there should be waves in the ether other than light waves that travel at the speed of light.
2. Hertz, 1880s, produced radio waves, which behaved just as Maxwell had predicted.
4. Maxwell’s accomplishment
1. Maxwell demonstrated a mechanism by which people could understand the interrelations between phenomena.
2. Many physicists regarded his work as the greatest accomplishment since Newton.
5. Maxwell’s obscurity
1. His work is very difficult to read-highly mathematical and very complicated-and thus difficult to popularize.  (For a comparison of different forms, see http://hyperphysics.phy-astr.gsu.edu/hbase/electric/maxeq.html )
2. He was not as charismatic as many of the figures we’ve discussed.
3. His mechanical model for the ether was discarded in the early 20th century (one of Einstein’s accomplishments--to be discussed in LBST 304).