i§8oJ 
On Water and Air, 
333 
cause of this suspension, and not the horror of a vacuum ; 
since it is very certain,” he adds, “ that there is more air to 
weight on it at the bottom than at the top : while we can- 
not say that nature abhors a vacuum at the foot of a 
mountain more than on its summit.” M. Perrier made the 
experiment. He found, as Pascal had predicted, that the 
mercury descended as he ascended the mountain, and as he 
came back again the column ascended, because of the aug* 
mented pressure of the atmosphere. 
I will just say one or two words with regard to the next 
great step made in this field. It was a step made by that 
grand old fellow whom so many of our hearers have reason 
to know, — the burgomaster of the town of Magdeburg, in 
Prussia —Otto von Guericke. This Otto von Guericke, who 
was the first to make the eledtric machine with a ball of 
sulphur which he rubbed in his hands, devised a means of 
exhausting the air, or taking the air out of a body. . The 
original instrument invented by him for this purpose is still 
preserved in the city of Berlin. 
Another illustration of the weight of the air I wish to 
give you here. Here is a very strong tin cylinder. I will 
extract the air from within that cylinder, and by-and-bye 
you will find that when the pressure within is withdrawn 
the pressure of the air outside will crush the vessel. [When 
the exhaustion of the air had proceeded for a shoit time the 
tin cylinder suddenly collapsed.] 
Now, I want to direct your attention to an experiment 
bearing upon the result obtained by the gaideneis at 
Florence. Here you see I have a tube 5 feet long. The 
pressure of the atmosphere lifts the water in that tube so as 
to fill it, although the same pressure is. not competent to 
support a column of mercury of that height. 1 his tube is 
prolonged by means of another tube to the base of the 
building, so that between the top, the glass tube, and the 
base of the building there is a distance of 33 feet. From 
the interior of the tube we exhaust the air, and the pressuie 
of the atmosphere upon the surface of the liquil contained 
in the basin where this tube ends downstairs, forces the 
liquid up the tube as the vacuum is made. The water 
reaches a certain point, and then, according to the result 
enunciated by Galileo, beyond that point it cannot go. It 
reaches a point where the pressure of the atmosphere upon 
the basin down stairs is exactly equal to the weight of the 
column of water that we raise. 
