A HISTORY OF SCIENCE 



1643. In describing this invention he says: "Making 

 choice of a large, thin, and light glass bubble, blown 

 at the flame of a lamp, I counterpoised it with a metal- 

 lic weight, in a pair of scales that were suspended in a 

 frame, that would turn with the thirtieth part of a 

 grain. Both the frame and the balance were then 

 placed near a good barometer, whence I might learn the 

 present weight of the atmosphere; when, though the 

 scales were unable to show all the variations that ap- 

 peared in the mercurial barometer, yet they gave notice 

 of those that altered the height of the mercury half a 

 quarter of an inch." 3 A fairly sensitive barometer, 

 after all. This statical barometer suggested several 

 useful applications to the fertile imagination of its 

 inventor, among others the measuring of mountain- 

 peaks, as with the mercurial barometer, the rarefica- 

 tion of the air at the top giving a definite ratio to the 

 more condensed air in the valley. 



Another of his experiments was made to discover 

 the atmospheric pressure to the square inch. After 

 considerable difficulty he determined that the relative 

 weight of a cubic inch of water and mercury was 

 about one to fourteen, and computing from other 

 known weights he determined that "when a column 

 of quicksilver thirty inches high is sustained in the 

 barometer, as it frequently happens, a column of air 

 that presses upon an inch square near the surface of the 

 earth must weigh about fifteen avoirdupois pounds." 

 As the pressure of air at the sea-level is now estimated 

 at 14.7304 pounds to the square inch, it will be seen 

 that Boyle's calculation was not far wrong. 



From his numerous experiments upon the air, 



206 



