"Learn to deprive large masses of their gravity and give them absolute levity, for the sake of transport."
Benjamin Franklin
Magnetically levitated (maglev) trains glide above a track, propelled by superconducting electromagnets. The principle is more than a century old, but initially the huge electrical currents needed to provide a sufficiently strong magnetic field were impractical. The breakthrough came when two physicists, Gordon Danby and James Powell, at Brookhaven National Laboratory decided to use high temperature superconductors as electromagnets. They obtained a patent for the technology in 1968, and by 1979 visitors to a transportation exhibition in Hamburg, Germany, were enjoying a short test run on a Transrapid maglev train.
Maglev trains need a guiding track and the carriages float just above it. Changing the field produced by the electromagnets in the guideway pulls the train along. The only friction is due to air resistance, so extremely high speeds are possible. Changes in field strength can produce very high accelerations, and much more variable track gradients can be accommodated than with normal trains, so cuttings and embankments would not be needed.
There are serious disadvantages to maglevs. The guideways are extremely expensive, and the trains cannot be diverted from the maglev track to normal railways to take in existing inner city termini.
Maglev trains were introduced in the United Kingdom in 1984, linking Birmingham airport to the nearby railway station. In China, another system links Shanghai to Pudong International Airport. The success of the TGV trains that run on normal track, however, has reduced the appeal of maglev.
