A Max Kohl Earth Inductor or Delzenne Circle is a flip coil used to measure the magnitude and direction of the earth’s magnetic field. The rotating coil is quickly flipped through 180 degrees, and the output is fed to a ballistic galvanometer. This device, with a long period of oscillation, measures the total charge delivered by the induced EMF; the charge is then proportional to the magnitude of the magnetic field threading the coil.
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Van Leest Antiques
Van Leest Antiques, based in Utrecht in the Netherlands, specialises in antique scientific and medical instruments. Their collection covers mainly scientific and medical antique instruments: barometers, globes and planataria, nautical instruments, anatomical models, and pharmacy items. Toon Van Leest travels regularly in Europe and visits trade fairs, auctions, and antique dealers to collect stock and to find pieces to fulfil his clients' unusual requests.
As well as being an avid antique collector and dealer, Toon Van Leest is also a dentist. He believes that antiques are a stable investment, not reliant on trends or fashion, and have truly lasting value. Above all, he says, antiques are timeless and never lose their beauty.