near Clermont in Auvergne, which should silence con- 

 troversy. Two tubes filled with mercury, the columns 

 of equal heights, were carried to the foot of the moun- 

 tain, one of which was left there standing at 28 inches, 

 and the other taken to the summit ; as they ascended, 

 the mercury in the tube gradually sunk until it stood at 

 24' 7 inches; as they descended, the mercury as gra- 

 dually rose again ; and when placed by the side of the 

 tube left below, their elevations coincided. As Pascal 

 had anticipated, in ascending the mountain the weight 

 of a portion of the column of the atmosphere equal to 

 the height of the mountain being removed from the sur- 

 face of the mercury in the bason, that which was in the 

 tube fell, until its weight was again counterpoised by the 

 atmosphere ; and conversely in descending, the weight 

 of the column of the atmosphere being increased by the 

 weight of the portion equal to the height of the moun- 

 tain, pressed upon the mercury in the bason, and forced 

 it to ascend in the tube until both weights balanced 

 each other. 



Pascal originated the idea of measuring elevations by 

 the variations of the barometer, but he foresaw a diffi- 

 culty. He compared the atmosphere to a mass of wool, 

 the lowest parts of which were more pressed than those 

 above ; and his sagacity led him to the fact, that from 

 the dilatation of the atmosphere the rise and fall of the 

 mercurial column would not be equal through equal 

 spaces. This concluded his philosophical inquiries ; he 

 afterwards turned his attention to the'ology. 



In 1666 Boyle discovered that the atmosphere was 



B2 



