360 FRAGMKNTS OF SCIKNUti. 



rises in a pump; the effect being then explained by the 

 maxim that " Nature abhors a vacuum." It was not known 

 that there was any limit to the height to which the water 

 would ascend, until, on one occasion, the gardeners of 

 Florence, while attempting to raise water to a very great 

 elevation, found that the column ceased at a height of 

 thirty-two feet. Beyond this all the skill of the pump- 

 maker could riot 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 circum- 

 stances, was such a pressure to be 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 analyze. It is by a kind of inspira- 

 tion 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 equi- 

 librium, a shorter column of a heavier liquid ought to do 

 the same. Now, 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 sub- 



