240 THE WORLD MACHINE 



invention is commonly attributed to Ctesibius, the forerunner 

 of Hero in Alexandria. Probably it was known in a crude 

 way thousands of years before that. To explain its action the 

 ancients had invented the idea that nature had a horror of a 

 vacuum, and that if in any way a vacuum was created, what- 

 ever of a material nature lay next would rush in to fill the 

 emptiness. It is evident enough from the pages of Lucretius 

 that they had a clear idea of the weight of the air ; but, so 

 far as we know, it never occurred to them to connect the 

 pressure of the air with the action of the pump. The simple 

 binding link escaped even Galileo himself another of the thou- 

 sands of instances which might be adduced showing the sharp 

 delimitations even of the most piercing and far-seeing minds. 



It is told that some workmen, in constructing a house near 

 Florence, had put down a rather long pipe and discovered that 

 it would not work. The water would rise in the pump to a 

 height of about thirty-two feet and no more. When Galileo 

 was asked about it he simply made a jest. He loved a fling at 

 the ancients ; and observing that evidently nature had a horror 

 of a vacuum only to a height of thirty-two feet, gaily went 

 his way. Still he and his disciples must have discussed the 

 subject ; and how keen a joy it must have been to these young 

 men to talk the new things over with the man who was creating 

 the most of them. 



One of these Galilean disciples was Torricelli. Pondering over 

 the matter, Torricelli came to the conclusion that if the air would 

 sustain a column of water about thirty-three feet high, it would 

 hold up other liquids in proportion to their weights ; as mercury 

 is fourteen times as heavy as water, the column of mercury 

 that it would sustain would be only one-fourteenth as high. 

 Viviani tried it and showed that his friend's expectations were 

 correct. The meaning of it all was very clear. Air and the 

 mercury, or air and the water simply formed a balance : the 

 weight of the air was equal to the weight of the column it 

 sustained. 



Torricelli's discovery came in the year that followed his 

 master's death. It excited the liveliest interest ; the news of 

 it travelled fast. In France it reached the ears of twenty years 

 old Blaise Pascal, already revealed as a mathematical genius of 

 the highest order. It could have been but a rumour, for he 

 repeats the experiments in a great variety of ways ; he makes 



