114 SEVENTEENTH CENTURY. PT. I1L 



CHAPTER XV. 



SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 



Torricelli Perrier Pascal Otto Guericke Foundation of Royal 

 Society of London and other Academies of Science. 



Torricelli's Invention of the Barometer, 1644. We 



must now turn to quite another subject on which new light 

 was being thrown at this time. Among the many different 

 mechanical experiments which Galileo made during his life, 

 there had been one with a common pump which puzzled 

 him very much, and which he had never been able to 

 explain. 



You know that if you put the mouth of a squirt in water 

 and pull back the handle, the water rises up into the tube. 

 That is to say, as soon as you leave a space inside the squirt 

 quite empty without any air in it, the water rushes in. 

 In the same way, water may be made to rise up a long 

 tube standing with its open end in a pond or basin, by 

 drawing up a tight-fitting stopper A, Fig. 14, called a piston, 

 and so driving the air out at the top and leaving a vacuum 

 inside the tube. But Galileo noticed that as soon as the 

 water had risen up to the height of about 34 feet it would 

 not mount any higher, even though the tube between the 

 surface of the water c, and the piston A, had no air in it. 

 He could not, however, find out why the water should stop 

 rising just at this point, and it was not till after his death 



