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