24 FEAGMENT8 OF SCIENCE. 



the skill of the pump-maker could not get it to rise. 

 The fact was brought to the notice of Galileo, and he, 

 soured by a world which had not treated his science 

 over kindly, is said to have twitted the philosophy of 

 the time by remarking that nature evidently abhorred a 

 vacuum only to a height of thirty-two feet. Galileo, 

 however, did not solve the problem. It was taken up 

 by his pupil Torricelli, to whom, after due pondering, 

 the thought occurred, that the water might be forced into 

 the tube by a pressure applied to the surface of the liquid 

 outside. But where, under the actual circumstances, 

 was such a pressure to be 1 found? After much reflection, 

 it flashed upon Torricelli that the atmosphere might 

 possibly exert this pressure ; that the impalpable air 

 might possess weight, and that a column of water thirty- 

 two feet high might be of the exact weight necessary to 

 hold the pressure of the atmosphere in equilibrium. 



There is much in this process of pondering and its 

 results which it is impossible to analyse. It is by a kind 

 of inspiration that we rise from the wise and sedulous 

 contemplation of facts to the principles on which they 

 depend. The mind is, as it were, a photographic plate, 

 which is gradually cleansed by the effort to think rightly, 

 and which, when so cleansed, and not before, receives 

 impressions from the light of truth. This passage from 

 facts to principles is called induction ; and induction, 

 in its highest form, is, as I have just stated, a kind of 

 inspiration. But, to make it sure, the inward sight 

 must be shown to be in accordance with outward fact. 

 To prove or disprove the induction, we must resort to 

 deduction and experiment. 



Torricelli reasoned thus: If a column of water thirty- 

 two feet high holds .the pressure of the atmosphere in 

 equilibrium, a shorter column of a heavier liquid ought 

 to do the same. Now, mercury is thirteen times heavier 



