THE ATMOSPHERE. 63 



The first vacuum obtained by mechanical means, 

 was that of Otto de Guericke, a burgomaster of Mag- 

 deburg, who, in the year 1654, removed the air from two 

 hemispheres, by the use of a syringe. The experi- 

 ment he wished to exhibit was the pressure of the air. 

 In this he succeeded, for the continued efforts of twelve 

 horses, pulling in opposite directions, could not overcome 

 the power by which the hemispheres were pressed to- 

 gether. 



If we place an inverted tumbler, whose edge has 

 been ground, upon the plate of the pump, and exhaust 

 the air, it will be so firmly fixed as to be difficult of re- 

 moval. The power required to raise the tumbler, will 

 be equal to the number of square inches it covers, mul- 

 tiplied by fifteen pounds. 



The airpurnp and barometer reciprocally prove each 

 other. The barometer, showing when the air has been 

 removed from a vessel, by the entire fall of the quick- 

 silver; and the airpump proving the fluid is supported 

 by the air, by this operation. 



A great number of experiments may be exhibited by 

 the airpump, which the limits of our number will not 

 allow us to describe. Besides it is our object rather to 

 explain principles than to dwell on particulars. 



The cause by which water is generally supposed to 

 be raised in a pump is called suction. But there is 

 not a single instance where it is supposed to prevail, 

 which cannot be explained by the pressure of the air. 

 The term suction is too vague and indefinite for any 

 philosophical purpose, and blinds us to those beauties 

 which nature has presented. The effect from which this 

 appellation will be the most difficult of removal, is that 

 produced by the mouth. Sucking poisoned wounds is 

 coeval with the remotest antiquity, and although the 

 term conveys to our minds a certain operation, yet it 

 does not reveal to us its real features. The applica- 

 tion of this word to the process of drinking, would be 

 considered highly vulgar, yet it is performed on pre- 

 cisely the same principle, and in a manner similar to 



