MIRACLES AND SPECIAL PROVIDENCES. 25 



Torricelli reasoned thus: If a column of water 

 thirty-two feet high holds the pressure of the at- 

 mosphere in equilibrium, a shorter column of a heavier 

 liquid ought to do the same. No\v, mercury is thirteen 

 times heavier than water; hence, if my induction be 

 correct, the atmosphere ought to be able to sustain only 

 thirty inches of mercury. Here, then, is a deduction 

 which can be immediately submitted to experiment. 

 Torricelli took a glass tube a yard or so in length, 

 closed at one end and open at the other, and filling it 

 with mercury, he stopped the open end with his thumb, 

 and inverted it into a basin filled with the liquid metal. 

 One can imagine the feeling with which Torricelli re- 

 moved his thumb, and the delight he experienced on 

 finding that his thought had forestalled a fact never 

 before revealed to human eyes. The column sank, 

 but it ceased to sink at a height of thirty inches, leav- 

 ing the Torricellian vacuum over-head. From that 

 hour the theory of the pump was established. 



The celebrated Pascal followed Torricelli with an- 

 other deduction. He reasoned thus: If the mercurial 

 column be supported by the atmosphere, the higher we 

 ascend in the air, the lower the column ought to sink, 

 for the less will be the weight of the air overhead. He 

 caused a friend to ascend the Puy de Dome, carrying 

 with him a barometric column; and it was found that 

 during the ascent the column sank, and that during 

 the subsequent descent the column rose. 



Between the time here referred to and the present, 

 millions of experiments have been made upon this sub- 

 ject. Every village pump is an apparatus for such ex- 

 periments. In thousands of instances, moreover, 

 pumps have refused to work; but on examination it 

 has infallibly been found that the well was dry, that 

 the pump required priming, or that some other defect 



