SUCKERS. 



331 



its centre, so as to allow a string to be attached. The leather 

 is then soaked in water until it is quite soft. If it be firmly 

 pressed on any smooth object, such as a stone, the air is 

 forced from under it, and it becomes capable of sustaining a 

 weight in proportion to its dimensions. As the air has a 

 pressure of about fifteen pounds on every square inch, it is easy 



SUCKERS OF CUTTLB. 



LIMPET. 



STAR-FISH. 



SUCKING-FISH. 



FOOT OF OECKO. 



LAMPERN. 



CUPPING-GLASS. 



PNEUMATIC PEG. 



SUCKER. 



11AGOBBURG HEMISPHERES. 



to calculate the weight which it will uphold, a margin being 

 left for imperfection of vacuum. 



The lower figure represents the instrument called the 

 Magdeburg Hemispheres, which are made for the purpose 

 of showing the enormous power of air-pressure. They are 

 two hollowed hemispheres, having their edges very accurately 

 ground together. When used, a little lard is rubbed on the 

 edges in order to insure their exact fit, and they are then 



