Toricelli mercurybarometers measure continiously the changes in airpressure. To estimate forecasts, one has to set the index on the glass tube to the actual mercurylevel. The tendancy of the atmospheric airpressure and the amount of change make a reliable forecast possible..
Evangilista Toricelli was an Italian Scientist in the seventeenth century (1608-1647). He was looking for a way to prove that the air had a certain weight.
He took a glass tube, enclosed at one side, and filled that tube completely with mercury. Now all air was out of the tube. He locked the tube on the open side with his thumb and turned the tube upside down in a reservoir, filled with mercury. Now he released his thumb und he noticed that a certain amount of mercury was kept in the tube. The airpressure on the surface of the mercury in the reservoir pushed the mercurycolumn up and down in the tube.
He noted an average height of 76 centimeters after repeating the experiment. One other observation was, when the column mercury went down, the weather went bad, and when the mercury climbed up in the tube, the weather changed to fair. This was the birth of the first actual and reliable weatherinstrument.
Medford Clock & Barometer, 3 Union Street, Medford, NJ 08055
Phone: (609) 953-0014, Fax (609) 953-0411
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