PROPERTIES OF GASES 89 



alcohol, the alcohol will rise higher in the tube than 34 ft., 

 because it will take more fluid to balance the weight of the 

 air. If the fluid were heavier than water, as is quicksilver 

 or mercury, it would not rise so high, because it would require 

 less of it to equal and balance the weight of air. 



88. History of the Barometer. In 1643, more than two 

 hundred years ago, an Italian, named Torricelli, filled a glass 

 tube, 33 in. long and open at one end, with mercury. Putting 

 his finger over the open end so as to keep the mercury from 

 falling out, he turned it bottom upward into a bowl of mer- 

 cury, and then removed his finger. As mercury is one of 

 the heaviest things in the world, it would seem as if it should 

 have run out of the tube into the bowl; yet it only fell a 

 little way, and then remained standing in the tube. As 

 mercury is about fourteen times heavier than water, Tor- 

 ricelli saw that the height of the mercury in the tube was 

 about -fj part of the 34-ft. column of water. He at once 

 concluded that the mercury was held up by the pressure of 

 air on the surface bowl. He afterward noticed that the 

 mercury did not always stand at the same height, but that 

 it rose and fell with the changes in the weather, the air pres- 

 sure decreasing in damp, wet weather and increasing in dry, 

 fine weather. This led to the making of the barometer, 

 which is the same in principle as the tube used by Torricelli. 



89. Kinds of Barometers. The barometer in its simplest 

 form consists of a long inverted vacuum tube, sealed at the 

 upper end. The lower end dips into a cup of mercury. A 

 graduated scale on the side of the tube measures the rise 

 and fall of the mercury. Such an instrument is often used 

 to Determine the height of mountains and other high places, 



