MIRACLES AND SPECIAL PROVIDENCES. 25 



than water ; hence, if my induction be correct, the at- 

 mosphere 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 removed 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, leaving the Torricellian 

 vacuum over-head. From that hour the theory of the 

 pump was established. 



The celebrated Pascal followed Torricelli with another 

 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 in- 

 fallibly been found that the well was dry, that the pump 

 required priming, or that some other defect in the 

 apparatus accounted for the anomalous action. In every 

 case of the kind the skill of the pump-maker has been 

 found to be the true remedy. In no case has the 

 pressure of the atmosphere ceased ; constancy, as regards 



