VOL. I.] PHILOSOPHICAL TRANSACTIONS. 55 



a glass tube filled with mercury, hermetically sealed at one end, with the 

 other end open, and immerged in stagnant mercury. The barometer was first 

 made public by Mr. Boyle, and employed by him and others to discover all the 

 minute variations in the pressure and weight of the air. With this instrument 

 he made many observations in 1659 and 1660, before any others were public 

 or heard of by him. 



Dr. Beal is so well pleased with the discoveries already made with this in- 

 strument, that he looks upon it as one of the most extraordinary inventions in 

 the world. " Who could have thought (says he) that men should find an art 

 *' to weigh the air that hangs over their heads in all its changes ; and even 

 '^ distinguish by weight the winds and clouds? Or, who could have imagined 

 *' that the clearest air is the heaviest, and the thickest air, when loaded with 

 " clouds, ready to dissolve and fall, should then be the lightest?" Hence the 

 doctor descends to particular observations. 



And first, he says, he could never fill his wheel-barometer so exactly with 

 mercury as to exclude all air; and therefore he depended more on the mer- 

 curial cylinder, from which he took all his notes. Its length is but 35 inches, 

 of a narrow bore, and a thick glass. 



1. In all his observations from May 28, 1664, to December 9, l665, the 

 quicksilver ascended but very little above 30^ inches. 



3. It ascended seldom so high as that, especially on December 13, 1664, 

 the weather being changeable, and the evening fair. 



4. By his calendar of June 22, 1664, at five in the morning, in a long 

 tract of fair settled weather, the mercury ascended about half an inch higher 

 than 30. So that the mercury may rise as high in the hottest summer as in 

 the coldest winter. 



5. He had observed it ascend higher in cold weather ; and very often both 

 in winter and summer to be higher in the cold mornings and evenings than in 

 the wanner mid-day. 



6. Generally, in settled and fair weather, both winter and summer, the mer- 

 cury is higher than a little before, or after, or in rainy weather. 



7. Again, it descended generally lower after rain than it stood before rain. 



8. It falls also generally in great winds, and it seemed to sink a little upon 

 opening a wide door to let in stormy wind* : Yet he found it to continue very 

 high in a long stormy wind of three or four days. 



9. Again, it is generally higher in an east and north wind than in a south 

 and west wind. 



10. He tried several times to alter the air in his closet by fumes and thick 

 smoaks ; but the mercury seemed not to be affected more than what might 



