MATHEMATICAL SCIENCES SEVENTEENTH CENT. 169 



FIG. 71. BLAISE PASCAL. 



liquid in the basin. This confirmed Torricelli's explanation, and 

 abolished at once such notions as suction or Nature's abhorrence of 

 a vacuum. But the experiment created not a little controversy, for 

 the mercury, in descending from the top of the tube, leaves behind 

 it the space known as the Torricellian Vacuum. This vacuum was a 

 stumbling-block to some of the philosophers of that day, and a great 

 dispute arose as to whether Torricelli was right in affirming that the 

 column of mercury was sustained by the pressure of the atmosphere. 

 Torricelli, however, soon remarked certain variations in the height of 

 the column of mercury, and he did not hesitate to attribute these to 

 variations in the atmospheric pressure. We need hardly remind the 

 reader that Torricelli had, in fact, invented the Barometer, that in- 

 strument which has proved of vast utility by giving us the means of 

 measuring the variations of the atmospheric pressure. 



The doubts which had been entertained as to Torricelli's explanation 

 were soon set at rest by some experiments instituted by the celebrated 

 BLAISE PASCAL(i623 1662), then a very young man residing at Rouen. 

 Pascal, having learnt the details of Torricelli's experiment, resolved 



