co i Signs of Weather [Book V. 



times in conjunftion with the weight, fo as to increafe 

 the effect of it ; at other times it acts in a contrary 

 way, and may aifo diminifh, or even counterbalance, 

 the effect of the augmentation of weight. It follows, 

 then, that fine or bad weather may continue, however 

 high the mercury may be in the barometer j and ft ill 

 this does not weaken the explanation which has before 

 been given of this fact. 



Obfervation, however, in thefe cafes is always pre- 

 ferable to theory ; and from long and attentive ob- 

 fervation, and from a careful infpection of thole of 

 other philofophers, Mr. Adams was enabled to lay 

 down the following -principles in his ufeful treatife on 

 this inftrument. 



1. It generally happens, that, when the mercury in 

 the tube falls, the air being lighter, it will depofit its 

 vapour, and produce rain : but when it rifes, the air 

 being heavier, the vapours will be fupportedj and fine 

 weather is the ufual confequence. 



2. When the mercury falls in frofty weather, either 

 fnow or a thaw may be expected j but if it riles in 

 the winter with a north or eaft wind, it generally fore- 

 bodes a froft. 



3. It is neceflary to attend to the progrefs of the 

 rife and fall 3 thus, if it finks flowly, the rain may be 

 expected to be of fome continuance. In the fame 

 manner, when the mercury riles gradually, we may 

 be inclined to believe, that the fine weather will be 

 lafting. 



4. When the barometer is fluctuating, rifing and 

 falling fuddenly, the weather may be expected to be 

 like it, changeable. 



5. When it falls very low, there will be much rain. 



6. But if its fall is low and fudden, a high wind fre- 

 quently follows. 



7. When 



