Mifcellanea Curiofa. 8 1 



A Dijcourfe of the Rule of the De- 

 creafe of the height of the Mer- 

 cury in the Barometer^ according 

 as Places are elevated above the 

 Surface of the Earth ; with an 

 Attempt to difcover the true Rea- 

 fon of the Rifing and Falling of 

 the Mercury , upon Change of 

 Weather. By Edm. Halley. 



TP H E Elaftlck Property of the Air has 

 X been long fmce made out, by Experiments 

 before the Society % and elfewhere ; and 



the Refinance of its Spring is' found to be near* 

 ly equal to the Weight or Force that compre£ 

 fes it ; as alfb, that the Spaces the fame Air oc- 

 cupies, under differing Preflures, are recipro- 

 cally as thofe Preffiires : It has been (hewn like- 

 wife by undoubted Experiment, that the fpeci- 

 fick Gravity of the Air, near the Earth's Sur- 

 face to that of Water, was once as i to 840 • 

 again as 1 to 8?x ; and a third time, in a very 

 large VefTel holding 10 Gallons, as 1 to 860 • 

 all which, confidering the Difficulty of the Ex- 

 periment, agree well enough, the Mercury (land- 

 ing at all thofe times about 19 Inches I ■ But 

 by Reafon 'twas Summer-weather, and confe- 



G qumtly, 



