THE BAROMETER. 



AMONGST the ancient philosophers there was a physical dogma adopted, 

 viz., nature abhors a vacuum. This arose from their observing, that the 

 moment a solid or a liquid was by any means removed, immediately the 

 surrounding air rushed in and filled the space which the solid or liquid 

 had previously occupied. It is said that for two thousand years the 

 ascent of water in pipes, pumps, &c., was all accounted for by this suppo- 

 sition of nature's abhorrence of a vacuum, when it happened that some 

 engineers employed at Florence to raise water from what at that time was 

 considered an unusually great depth, found that the water would rise no 

 higher than about thirty two feet above the surface of water in the well. 

 It is said that Galileo, the most celebrated philosopher of that day, was con- 

 sulted in this difficulty, and that his answer was, that *' Nature's abhorrence 

 of a vacuum extended only to the height of thirty two feet, but that 

 beyond this her disinclination to an empty space did not extend." 

 Some writers, however, deny this statement; while, on the other hand, 

 others admit it, but think it to have been ironical. It is certain, however, 

 that Galileo directed his attention to the point, experimented on it 

 greatly, and soon saw the absurdity of the maxim, that " nature abhors 

 a vacuum. " The problem was successfully solved by Torrecelli, the pupil 

 of Galileo; he argued thus: Whatever be the cause which sustains a 

 column of water in a common pump, the measure and the energy of that 

 power must be the weight of the column of water, and, consequently, if 

 another liquid be used heavier or lighter, bulk for bulk, than water, then 

 the same force must sustain a lesser or greater column of such liquid. 

 Upon this reasoning, he tried experiments upon various liquids, and, 

 amongst others, mercury, which is the heaviest liquid known, being about 

 13 times heavier than water; it follows, therefore, that the height of a 

 column of mercury must be 13j times less than a column of water which 

 would be sustained by the same cause. Hence he computed that the heigh t 

 of the column of mercury would be about 18 inches. To prove this, he 

 procured a glass tube upwards of 30 inches in length, and closed at one 

 end, and having filled it with mercury and placed his finger on the open 

 end, he plunged it into a vessel containing mercury; instantly, on the remo- 

 val of his finger, the mercury gradually fell in the tube, and finally stood 

 at the height of about 28 inches. This experiment immediately showed 



