56 THE REALITIES OF MODERN SCIENCE 



fell away from the top of the tube until its column was 

 about 30 inches high, i.e. about one thirteenth of 32 

 feet. 



The theory received further support very shortly 

 from an experiment by Pascal. He reasoned that if 

 the barometer was carried up a mountain so as not to 

 be so deep in the ocean of air at the bottom of which 

 we live, then the pressure of the air should be smaller 

 and it should be unable to sustain so high a column of 

 mercury. At his suggestion his brother-in-law tried 

 the experiment on Puy de Dome, and wrote back to 

 Pascal that he was " ravished with admiration and 

 astonishment" when he found that after he had as- 

 cended the mountain for about three fifths of a mile 

 the mercury column was three inches shorter. Of 

 course, if an air pump had been available Torricelli's 

 theory might have been checked as in classrooms to-day 

 by surrounding both the tube and the basin of mercury 

 by a glass vessel and then evacuating the latter. If 

 the experiment is performed it will be found that as 

 the air is removed the barometer column sinks until 

 it is level with the surface of the mercury in the basin. 

 As air is allowed to reenter the vessel the column rises 

 to its original height. 1 



The balance, Torricelli's barometer, and the air 

 pump, which followed shortly, are three of the scientific 

 instruments which made possible much of the experi- 

 mental work of the last 300 years. The microscope 

 and the telescope, the latter invented by Galileo, have 



1 Boyle performed this experiment in 1659, five years after von 

 Guericke invented the air pump. Cf. Moore, "History of Chemis- 

 try," McGraw-Hill Book Co., 1918. 



