A microprocessor regulated the vacuum pump which was connected to the top end of the water barometer by a copper pipe. At ten minutes intervals, the vacuum pump was switched on, and evacuated the air form the 11.5 meter long glass pipe, causing the more than 12 metre tall instrument to fill with 55 litres of water within two minutes. Readings could then be taken at the second storey level of the museum. After five minutes, air was admitted in the pipe, such that water returned to the cistern in three minutes. A vacuum was then drawn again, etc. etc.
Visitors who wanted to take a reading, needed to climb ten metres of stairs first. Finally they reached a platform in the attic, just above the leaded glass cupola. Near the platform, the wooden plank was continued by a Perspex plate. There was a board on which the Vacuum Pump Cycle was explained, and the water temperature in the cistern was shown on a display.
The white Perspex register plate had two scales; centimetres above the water surface in the cistern and millibars or hectopascals. On the explanation board, a rule of thumb was given to make a correction for temperature. Water vapour pressure depresses the actual reading and this ‘error’ increases with temperature.
Every ten minutes, visitors could witness an interesting physical phenomenon, when they made the climb to the cupola area. At the moment the water reached it highest possible point in the pipe, the air pressure above the water had been lowered so dramatically, that the water started to boil spontaneously, although its temperature was just about 20 degrees! This ‘cold boiling’ was reinforced a bit by air bubbles that were formed in the water column. As soon as the pump stopped evacuating the pipe, the water level became calm within a couple of seconds, thus enabling the visitors to take a proper reading.
The Guinness Book of Records Certificate
With the giant barometer installed, press releases could be sent out to the media to announce the museum plans and the request to obtain antique barometers on loan. Within just a few months, there were enough barometers offered on loan to arrange the displays and the walls. Meanwhile Bert Bolle claimed to have built the largest barometer in the world, and when the International Guinness Book of Records recognized the claim, it was big news again.
