456 RECAPITULATION. 



10. Animals cannot live, nor will a candle bum, 

 in a vessel exhausted of air. 



11. The air presses upon every body immersed 

 in it, and on every side. 



12. The rise of water in pumps is owing to the 

 air on one part of the water being removed, which 

 causes it to yield and be pressed upwards in that 

 part. 



13. Suction is an absurd notion, now exploded, 

 and accounted for from the pressure of the air. 



14. Barometers are instruments for measuring 

 the weight or pressure of the atmosphere. 



15. The Torricellian vacuum is the empty space 

 in the upper part of a barometer tube. 



16. Air may be condensed, or made to occupy 

 less space. 



17- The machines used for this purpose are 

 called condensers. 



18. Air in motion constitutes "wind. 



19. Machines for measuring the force of the 

 wind are called wind-gages. 



20. Sound is a vibratory motion of the air. 



21. An echo is the reflection of a sound. 



ABSTRACT OF HYDRAULICS. 



1. Hydraulics teaches the laws of fluids in 

 motion, 



2. The velocity of spouting fluids is as the 

 square root of the depth of the orifice below the 

 surface. 



3. Water in bended pipes always rises as high 

 as the source from whence it springs : hence the 

 construction of jets, or fountains, and the sup- 

 plying of towns with water. 



