t IX8TBUM*XTS OOKNKTE1) WITH H.t ll>s. 



water only to a height of 34 feet; for when this height is reached, the water 



i DO further, and thU shews either that the pressure of the atmosphere is 

 tabooed by that of the column of water, or else thut Nature has become 

 reconciled to a vacuum. 



From this time the production of a vacuum became the scientific object 

 ^jin^d at by a greet number of inventors. Torricelli, the pupil of Galileo, in 

 Irtl'i made the greatest step in this direction, by filling with mercury a tube 

 cloud at one end and then inverting the tube with its open end in a vessel 

 ef mercury. If the tube was long enough the mercury fell, leaving an empty 

 1PQQ* at the top of the tube. The vacuum obtained by filling a vessel with 

 ^JJLMIIJ jfiA removing the mercury without admitting any other matter is hence 

 called the Torricellian vacuum. Torricelli, therefore, gave us at once the mercury 

 pump and the barometer, though the subsequent history of these two instruments 

 w very different. 



A little before 1654 Otto Von Guericke, of Magdeburg, first applied the 

 principle of the common pump to the production of a vacuum. The fitting of 

 the pistons of the pumps of those days, however, though sufficiently water-tight, 

 was by no means air-tight. He therefore began by filling a vessel with WUUT 

 and then removing the water by a water-pump. In his experiments he met 

 with many failures, but he continued to improve his apparatus till he could 

 not only exhibit most of the phenomena now shewn in exhausted receivers, 

 but till he had discovered the reason of the imperfection of the vacuum when 

 water was used to keep the pump air-tight. 



"In the year 1658 Hooke finished an air-pump for Boyle, in whose laboratory 

 he was . an assistant ; it was more convenient than Guericke's, but the vacuum 

 was not so perfect ; yet Boyle's numerous and judicious experiments gave to 

 the exliausted receiver of the air-pump the name of the Boy lean vacuum, by 

 which it was long known in the greatest part of Europe. Hooke's air-pump 

 had two barrels, and with some improvements by Hauksbee it remained in use 

 until the introduction of Smeaton's pump, which, however, has not wholly 

 superseded it*." 



The history of the air-pump after this time relates chiefly to the con- 

 trivances for insuring the working of the valves when the pressure of the 

 remaining air is no longer sufficient to effect it, and to methods of rendering 



* Thomas Young's Lecture* on Nat. Phil (1807). Lecture xxx 



