Mifcellanea Curiofa. 9 1 



A fecond Caufe is the uncertain Exhalation and 

 Precipitation of the Vapours lodging in the Air, 

 whereby it comes to be at one time much more 

 crowded than at another, and confequently hea- 

 vier j but this latter in a great meafure depends 

 upon the former. Now from thefe Principles I 

 {hall endeavour to explicate the feveral Phenomena 

 of the Barometer^ taking them in the fame order 

 I laid them down. 



I. Why in calm Weather the Air being inclind 

 to the Mercury is commonly low ? I An- 



fwer, That the Mercury s being low, inclines it 

 to Rain ; for the Air being light, the Vapours 

 are no longer fupported thereby, being become 

 fpecifically heavier than the Medium wherein 

 they floated ; fo that they defcend towards the 

 Earth, and in their fall meeting with other 

 aqueous Particles t they incorporate together, 

 and form little drops of Rain ; but the Mer- 

 cury's being at one time lower than another, h 

 the effedl: of two contrary Winds blowing from 

 the place whence the Barometer ftands ; where- 

 by the Air of that place is carried both ways 

 from it, and confequently the incumbent Cylin- 

 der of Air is diminifhed, and accordingly the 

 Mercury (inks ; as for Inftance, if in the Ger- 

 man Ocean it mould blow a Gale of Wefterly 

 Wind, and at the fame time an Eafterly Wind 

 in the Irift* Sea ; or if in France it fliould blow 

 a Southerly Wind, and in Scotland a Northern ; 

 it muft be granted me, that That part of the 

 Atmefphere impendent over England^ would there- 

 by be exhaufted and attenuated, and the Mer- 

 cury would flibfide, and the Vapours which be- 

 fore floated in thole parts of the Air of equal Gra- 

 vity with themlelves, would fink to the Earth. 



2.. Why 



