116 DISSERTATION SECOND. [parti. 



water does not ascend in pntnps above a certain height, had 

 not discovered the true cause of the phenomenon. The 

 generosity of Torricelli was perhaps rarer than his ge- 

 nius ; — there are more who might have discovered the sus- 

 pension of mercury in the barometer, than who would have 

 been willing to part with the honour of the discovery to a 

 master or a friend. 



This experiment opened the door to a multitude of new 

 discoveries, and demolished a formidable idol, the honour 

 of a vacuum, to which so much power had been long attri- 

 buted, and before which even Galileo himself had conde- 

 scended to bow. 



The objections which were made to the explanation of 

 the suspension of the mercury in the tube of the barometer, 

 were overthrown by carrying that instrument to the top of 

 Puy de Dome, an experiment suggested by Pascal. The 

 descent of the mercury showed, that (he pressure which 

 supported it was less there than at the bottom ; and it was 

 afterwards found, that the fall of the mercury corresponded 

 exactly to the diminution of the length of the pressing co- 

 lumn, so that it afforded a measure of that diminution, and, 

 consequently, of the heights of mountains. The invention 

 of the airpump by Olio Guericke, burgomaster of Magde- 

 burg, quickly followed that of the barometer by Torricelli, 

 though it does not appear that the invention of the Italian 

 philosopher was known 1o the German. In order to obtain 

 a space entirely void of air, Otto Guericke filled a barrel 

 with water, and having closed it exactly on all sides, began 

 to draw out the water by a sucking pump applied to the 

 lower part of the vessel. He had proceeded but a very 

 little way, when the air burst into the barrel with a loud 

 noise, and ils weight was proved by the failure of the ex- 

 periment, as effectually as it could have been by its suc- 

 cess. After some other trials, which also failed, he 



