54 Experimental Philosophy. [Lecture 5. 



not this horror of a vacuum, or at least, that it , 

 was a very limited kind of a horror; for why 

 should Nature have a horror of a vacuum at one 

 height and not at another ? The matter was re- 

 ferred to the famous astronomer and philosopher 

 Galileo ; but in his time philosophical knowledge 

 was not sufficiently advanced to solve the diffi- 

 culty. 



The difficulty is, however, now explained, 

 through principles furnished by Galileo's pupil 

 Torricelli. We knoAv that a pump is a hollow 

 piece of timber or metal, to the bore of which a 

 piston, bucket, or sucker, is exactly fitted. That 

 the piston has a valve in it made with leather, 

 like the clapper of a bellows. When the piston 

 is pushed down, therefore, the air, or any fluid 

 contained in the pump, will force it open ; and 

 when the piston is drawn up, the pressure of the 

 air or water, which has been admitted in that 

 way, will keep the valve down. But to make the 

 matter perfectly clear, let us represent the opera- 

 tion in a glass model. In PI. VI. fig. 25, is a 

 pump constructed on the plan of a common, or 

 as it is usually called sucking pump. Let this 

 pump then, D, C, B, L. be immersed in water at 

 K ; in which case you will see the water rise as 

 high as L in the pipe or body of the pump. G is 

 the piston, sucker, or bucket, as it is sometimes 

 called, in which a is the valve ; and at H is a box 

 made similar to the bucket G with a valve in it 

 , with this difference, that the box H is immov- 



