THE ATMOSPHERE. 



and the water. " But nature abhors such a space," said the 

 ancients, "and therefore the water will not allow such a space 

 to remain unoccupied : we find accordingly that as the piston rises 

 the water follows it." By such fantastical theory pumps of various 

 lands were constructed. 



9. The antipathy entertained by Nature against an empty space 

 served the purposes of philosophy for a couple of thousand years, 

 when it happened in the time of Galileo, that is, about the middle 

 of the seventeenth century, that some engineers near Florence, 

 being employed to sink a pump to an unusual depth, found they 

 could raise by no exertion the water higher than 32 feet in the 

 barrel. Galileo was consulted, and it is said, that he answered, 

 half seriously, half sportively, that nature's abhorrence of a 

 vacuum extended to the height of 32 feet, but that beyond this 

 her disinclination to an empty space was not carried. The answer, 

 however, whatever it was, does not appear to have been satis- 

 factory, and the question continued to excite attention. 



10. After the death of Galileo, Torricelli, his pupil, since become 

 so celebrated, directed his attention to its solution. He argued, 

 that whatever be the cause which sustains a column of water in a 

 pump, the measure of the power thus manifested must be the 

 weight of the column of water sustained : and, consequently, if 

 another liquid were used, heavier bulk for bulk than water, the 

 same force would sustain a column of that liquid, having less 

 height in proportion as its weight would be greater. By using a 

 heavier liquid, therefore, such as mercury, for example, the column 

 sustained would be much shorter, and the experiment would 

 be more manageable. The weight of mercury being bulk for 

 bulk about 13| times that of water, it followed that, if the force 

 imputed to a vacuum could sustain 34 feet of water, it would 

 necessarily sustain 13^ times less, or about 30 inches of mercury.' 

 Torricelli therefore made the following experiment, which has 

 since become so memorable in the history of physical science. 



He procured a glass tube A B, fig. 2, more than 30 inches long, 

 open at one end, A, and closed at the other, B. Filling this tube 

 with mercury, and applying his finger at the open end A, so as t> 

 prevent its escape, he inverted it, plunging the end A into mercury 

 contained in a cistern, c D, fig. 2. 



On removing the finger, he observed that the mercury in the 

 tube fell, but did not fall altogether into the cistern ; it only sub- 

 sided until its surface E was at a height of about 30 inches above 

 the surface of the mercury in the cistern. 



This result, which was precisely what Torricelli had anticipated, 

 clearly demonstrated the absurdity of the statement imputed to 

 Galileo, that Nature's abhorrence of a vacuum extended to the 

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