AIR PUMPS AND APPARATUS. 



211 



The Air Shower. (Fig. 211.) This ap- 

 paratus consists of a block of wood, having 

 a long piece of wood, c, fixed lengthwise 

 through it, the under side of the block 

 being turned perfectly true, to fit the top 

 of a receiver, A. To use, place it in the re- 

 ceiver, A, which is also used as a hand glass, 

 place a tumbler of water, B, under, so that 

 the end of the wood is immersed in the 

 water ; place your thumb on the top of the 

 wood, and while the receiver is exhausting, 

 you will see the air pass out of the pores of the wood in*o 

 the water. Take off your thumb, and a vast stream of ait- 

 will flow through the wood. This experiment shows that 

 wood is pervious to air, and that the course of the air vessels 

 is lengthwise. Price, 75cts. ; receiver, 75cts. 



Mercury Shower. A pneumatic apparatus, Fij?- 2l ' 

 to show that, if the pressure of the atmo- 

 sphere be removed from an under surface, the 

 pressure still remaining on the surface above 

 has the effect of driving a fluid readily through 

 the pores of such substance as it would not 

 otherwise penetrate. A is a wooden cup. 

 B is a plug or nozzle of oak wood fastened 

 through the bottom of the cup and projecting 

 downwards two or three inches. C is a vessel 

 put beneath it when in use ; and D the open 

 topped receiver of an air pump. To use the 

 instrument, put a little mercury into A, and exhaust the ah 

 from D, when the mercury will soon filter through the oak 

 and fall into the cup C. 



Fig. 212, as above, consists of a mahogany cup, through 

 the bottom of which a solid piece of oak wood, about two 

 inches long, is fixed ; the bottom of the cup is fitted 

 air tight on the top of the receiver. The receiver used 

 for the hand, called the hand glass, is used for this 

 experiment. When mercury is poured into the cup, and 

 the air exhausted out of the receiver, the pressure of the at- 

 mosphere on the surface of the mercury in the cup, will 

 force it through the pores of the solid piece of wood, and 

 it will fall like a silver shower to the bottom of the bottle, 

 and the mercury be collected in a glass vessel beneath. In 



