ATMOSPHERE. 



2. One of the most direct demonstrations of the weight of tl 

 atmosphere is aiforded by the experiment, shown in all popular 

 lectures on physics, made with the apparatus called the Bladder 

 Glass. This is a glass cylinder of four or five inches in diameter, 

 open at both ends, upon one end of which a piece of bladder 

 rendered soft and pliable by being soaked in water, is firmly 

 tied, the wet edges of the bladder adhering to the outside surface of 

 the glass, and to its edge, so as to be in complete air-tight contact 

 with it. The end of the cylinder which remains uncovered is 

 then smeared at the edges with lard, and placed upon the plate of 

 an air-pump, the lard rendering its contact with the plate air- 

 tight. The air-pump, which will be described in another part 

 of this number, is nothing more than a syringe conveniently 

 mounted, by which the air can be partially or almost wholly, 

 extracted from any close vessel, the mouth of which is applied 

 upon the plate. 



Let us suppose then, that by the action of the pump, a part of 

 the air included under the bladder is withdrawn, the pressure of 

 the air thus rarefied will be less than that of the external air, 

 which is not so rarefied, and consequently the bladder being 

 pressed with more force downwards than upwards, will yield to 

 the excess of downward force, and will become concave. If by 

 the constant action of the pump more and more of the air bo 

 withdrawn, the excess of the downward force becoming greater 

 and greater, the bladder, if it have not sufficient strength to 

 support the increased pressure, will burst inwards with an 

 explosion as loud as that produced by the discharge of a large 

 pistol. 



3. The same effect will be produced in whatever direction the 

 mouth of the bladder-glass be presented, showing that the 

 pressure of the external atmosphere acts upon the bladder equally 

 in all directions downwards, laterally, obliquely, and upwards. 



4. Even to those who admit the great weight of a column of the 

 atmosphere, extending from the surface of the earth to the highest 

 limit of that fluid, this experiment performed in a room often 

 seems astonishing and inexplicable ; for however weighty may be 

 a column of air which extends upwards to the top of the atmos- 

 phere, it cannot be understood how a column extending upwards 

 only to the ceiling of the room can have so great a weight. It is 

 certain that water is much heavier than air, and that a column of 

 that liquid as high as the ceiling would not have a weight at all 

 comparable to that which bursts the bladder. 



This difficulty is explained by the common effect of fluidity, by 

 which pressure is equally and freely transmitted in all directions 

 through the fluid, which property was illustrated by the experiment 



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