ROBERT BGYLE. 



Otto Guericke, Consul of Magdeburg, had succeeded in empty- 

 ing glass vessels of their contained air, by sucking it out at the 

 mouth of the vessel, plunged under water. He alludes here to 

 Guericke's famous invention of the instrument now commonly 

 called the air-pump. This ingenious and ardent cultivator of 

 science, who was borne in Magdeburg, in Saxony, in the begin- 

 ning of the seventeenth century, in his original attempts to 

 produce a vacuum, used first to fill his vessel with water, which 

 he then sucked out by a common pump, taking care, of course, 

 that no air entered to replace the liquid. This method was 

 probably suggested to Guericke by Torricelli's beautiful 

 experiment with the barometrical tube, the vacuum produced 

 in the upper part of which, by the descent of the mercury, 

 has been called from him the Torricellian vacuum. It was 

 by first filling it with water that Guericke expelled the air 

 from the copper globe, the two closely-fitting hemispheres 

 comprising which six horses were then unable to pull asunder, 

 although held together by nothing more than the pressure of 

 the external atmosphere. 



This curious proof of the force, or weight of the air, which 

 was exhibited before the Emperor Ferdinand III., in 1654, 

 is commonly referred to by the name of the experiment of 

 the Magdeburg hemispheres. Guericke, however, afterwards 

 adopted another method of exhausting a vessel of its contained 

 air, which could be applied more generally than the one he had 

 first employed. This consisted in at once pumping out the air 

 itself. The principle of the contrivance which he used for that 

 purpose will be understood from the following explanation. If 

 we suppose a barrel of perfectly equal bore throughout, and 

 having in it a closely-fitting plug or piston, to have been 

 inserted in the mouth of the vessel, it is evident that, when 



