EVANGELISTA TORICELLI {1608-1647) 

 BLAISE PASCAL (1623-1662) 



These are two successors of Galileo as regards a part of his 

 work, and likewise forerunners of Guericke, as regards the 

 complete elucidation of the connection between atmospheric 

 pressure and the weight of the air. 



Both had only a short life. 



Toricelli was actually a pupil of Galileo's in his old age, 

 and became his successor as mathematician to the Grand 

 Duke of Tuscany. He was obviously a born experimenter. 

 This is already shown by his remark that small beads of glass, 

 which one can easily melt oneself, form excellent lenses of 

 high magnifying power; and many years later these were still 

 preferred to the compound microscope, which is much more 

 difficult to construct, and were used to make important dis- 

 coveries in the domain of the smallest forms of life. By 

 means of a series of quantitative experiments he discovered 

 the law, still named after him, of the flow of liquid fronx 

 openings in thin walls, whereby Galileo's laws of fall provea 

 to be valid in the simplest manner also for liquids. This was 

 the first law ever discovered concerning the motion of liquids 

 (hydrodynamics) as contrasted with the science of hydrostatics 

 founded by Archimedes. 



Toricelli's best known achievement was the construction 

 of the apparatus for measuring air-pressure, which was soon, 

 and is still called the barometer. Galileo had already mea- 

 sured this pressure, the 'power of the vacuum,' by means of 

 the height of the water column in the tube of a deep well in 

 Florence, and he had also calculated the much smaller height 

 of a column of copper which could be supported by the same 

 pressure. From this it was not far to the idea of trying a 

 mercury column, which, like the water column, could of 

 itself assume a height corresponding to the pressure to be 

 measured. Toricelli communicated his idea to his friend 



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