Institute and Museum of History of Science, Florence, ITALY

HORROR VACUI?
      "At the bottom of an ocean of air"        
Forecasting the weather More or less empty Accademia del Cimento (1657-1667)


Otto von Guericke's air-pump.
Otto von Guericke, Experimenta Nova (ut vocantur) Magdeburgica De Vacuo Spatio, Amsterdam 1672


Otto von Guericke's air-pump.
Otto von Guericke, Experimenta Nova (ut vocantur) Magdeburgica De Vacuo Spatio, Amsterdam 1672

The torricellian experiment of 1644 highlighted atmospheric pressure and demonstrated the existence of the vacuum.
Torricelli was convinced that the upper, closed part of the tube had to be empty. This was the first time that the existence of the vacuum had been claimed not at the level of pure speculation, but with the back-up of convincing experimental evidence.
Naturally, the torricellian vacuum was not a perfect vacuum, because mercury vapours stayed in the space created by the liquid metal's descent. It took only another ten years and the invention of the air-pump to succeed in making better and better vacuums, which encouraged experimentation.
Today we distinguish between various types of vacuum: the industrial vacuum, corresponding to 0.1 mmHg (1 mmHg=1 millimetre of mercury); the medium vacuum, up to 10-1 mmHg; the high vacuum, up to a 10-7; and lastly, the ultra vacuum, at less than 10-7 mmHg.
The procedures for producing the ultra vacuums up to 10-15 mmHg, needed for high speed particle colliders, are particularly complex. Even these vacuums are vastly inferior to the interstellar vacuum, which contains less than one atom every cm3.

 

 

 


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