60 



THE BAROMETER. 



the mercury in tlic cup must be most pressed by the air. It I 

 is true that in damp weather the air feels heaviest, but it is i 

 on account of its being less salubrious. The lungs under , 

 these circumstances do not play so freely, nor does the blood ] 

 circulate so well ; and thus obstructions are frequently occa- j 

 sioned in the smaller vessels, from which arise colds, asthmas, j 

 and fevers. The thinness of the air in elevated situations ] 

 is sometimes oppressive from being insufficient for respira- : 

 tion ; and the expansion which takes place in the more ; 

 dense air contained within the body is often painful. It oc- ; 

 casions distension, and sometimes causes the bursting of J 

 smaller blood-vessels. ,'i 



The barometer has been used for the purpose of measur- I 

 ing the heights of mountains and towers, and of estimating ] 

 the elevation of balloons. The weight of one hundred and I 

 three feet of air is equal to that of one tenth of an inch of j 

 mercury. If a barometer, therefore, be carried to any great ' 

 eminence, the mercury will descend one tenth of an inch for ; 

 every one hundred and three feet that the barometer ascends, j 

 When the surface of the mercury is convex, or stands higher ] 

 in the middle than at the sides, it is a sign the mercury is ^ 

 then in a rising state ; but if the surface be concave, or hollow ] 

 in the middle, it is then sinkiag. In very hot weather, the ^ 

 falling of the mercury indicates thunder. In winter, the = 

 rising indicates frost, and in frosty weather if the mercury ; 

 falls three or four divisions, there will be a thaw. But in a  

 continued frost, if the mercury rises, it will snow. In wet 

 weather, when the mercury rises much and high, and so \ 

 continues for two or three days before the bad weather is \ 

 entirely over, then a continuance of fair weather may be ex- ^ 

 pected. In fair weather, when the mercury falls low, and i 

 thus continues for two or three days before the rain comes, 

 then much wet weather may be expected and probably high '^ 

 winds. The unsettled motion of the mercury denotes un- < 

 settled weather. The words engraved on the scale are not 

 so much to be attended to, as the rising and falling of the 1 

 mercury. It always sinks lowest of all for great winds, • 

 though not accompanied with rain; but it falls more for 

 wind and rain together than for either of them alone. Ba- 

 rometers are frequently made of a tube with a curved neck 

 and bulb, being more commodious than the basin and tube. 

 ^0 make these tolerably exact, however, the circular are^ 



