Chap. 13.3 from the "Barometer. 501 



efpecially in the winter, that, during whole months, 

 every time that the mercury rifes in the barometer, 

 rain continues to fall ; and every time that it defcends, 

 fine weather returns. Still this may be reconciled to 

 what has been dated ; for fmce (as has been already 

 obferved) it is the great quantity of water ditfblved in 

 the air which augments its weight, if, therefore, during 

 rain, a new folution of water mould by any means be 

 effected in greater abundance than the quantity which 

 falls (and this we know may happen from various 

 caufes) the barometer will rife. If the water fo dif- 

 fblved remains in the lower region, this rife of the 

 barometer will predict a frefh fall of rain, which often 

 happens in fuch cafes. In fliort, if the air diffolyes 3 

 great quantity of water, and at the fame time cold, or 

 fome other caufe, mould impede that water from dif- 

 folving perfectly, and rifing to a great height, it will 

 augment the weight of the air in a proportionate de- 

 gree, and will caufe the barometer to rife j and in the 

 mean time it will be ready to be collected into drop, 

 and formed into rain, which will foon after take place. 

 "While this rain continues to fall, if there is no new 

 folution effected, the air will become lighter j the ba- 

 rometer will fall; and, notwithftanding that, it will 

 predict fine weather, which, according to this rule, 

 ought to happen. That kind of relation which appears 

 to fubfift between the weight of air and the change of 

 weather, according to circumftances, may be atrcou ited 

 for, therefore, in this manner. Fine weather may 

 happen, notwichitanding the diminution of the weight 

 of air, when fome other elaftic fluid, lighter than it, 

 becomes intermixed with it, without taking away the 

 tranfparency. In fhort, the elafticity of air, the force 

 oi' which may vary from different caufes, will Hill con- 

 tribute to vary its preffure. This elafticity acts fome- 

 K k 3 times 



