EVANGELISTA TORICELLI AND BLAISE PASCAL 49 



Viviani, Galileo's youngest pupil, who then first carried it 

 out in the year 1643, in which Galileo died. 



In this way it was possible to show in small dimensions, 

 and visibly by means of a glass tube, what the water column 

 in the well only allowed us to guess: the self-limited and feelf- 

 adjusting liquid column, which has the same pressure as the 

 atmosphere, and quite by itself leaves an empty space above 

 it; the possibility of such a thing had been for long regarded 

 with much doubt. Toricelli then repeated the experiment 

 with alterations, and made continued observations of the 

 height of the column, whereby he also became the discoverer 

 of the variability of atmospheric pressure. The publication 

 of these discoveries took place only in a letter, but at that time 

 this was not an unusual procedure, and sufficed to spread 

 the new knowledge, inasmuch as it has always remained 

 connected with the name of its discoverer. 



Blaise Pascal, who was born at Cleremont in the Auvergne, 

 already showed quite uncommon powers in early childhood. 

 He began to master Euclid at the age of twelve, wrote at 

 eighteen essays on conic sections of permanent value, and 

 also became early acquainted with Galileo's work. As soon 

 as he had learned enough concerning Toricelli's discovery of 

 the pressure of the air, it appeared to him of prime import- 

 ance to prove by a further series of experiments, that it is 

 actually the weight of the air which exerts the pressure and 

 holds up the mercury column. For this purpose he made a 

 special arrangement of two connected Toricellian tubes, so 

 arranged that one could remove the air supporting the other; 

 he then actually saw the latter fall down completely. When 

 air was readmitted, the column rose again. He also carried 

 out many experiments with apparatus provided with mercury 

 in flexible bags and sunk in siphon tubes under water, and 

 found that the pressure of the overlying water produces 

 exactly the same effects as those observed in Toricelli's tubes, 



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