1278 



Why the baro- 

 rometer varies 

 little near the 

 equator, and 

 very much in 

 high latitudes. 

 St. Helena. 

 Madras. 

 S. of Europe. 

 England. 

 1'eterfburgh, 



Thermometer j 



hygrometerj 



ele&rometer. 



The barometer 

 little efteemed 

 by farmers, be- 

 caufe the words 

 engraved thereon 

 are fallacious. 



Daily change in 

 the barometer, 

 ?nd why. 



OBSERVATIONS ON THE WEATHER. 



Upon thefe principles likewife we may account for the rife 

 and fall of* the barometer in the different zones. In the torrid 

 zone, particularly at St. Helena, and the iflands of the Pacific 

 ocean, it feldom varies more than three tenths ; at Madras 

 about five-tenths ; in the fouth of Europe not more than one 

 inch and two-tenths ; in England it varies two inches and a 

 half, and in Peteriburgh three inches four-tenths. In the two 

 firfl, the temperature of the atmofphere is not fubject to much 

 variation, and never to any great degree of condenfation. In 

 the third, reckoning from the tropics to the latitude of 40°, the 

 atmofphere may fometimes be fuddenly condenfed by currents 

 of cold air from the N. and ftill more fo in England. But the 

 greateft variation muftneceflarily take place on the continent 

 to the northward, where, during the fummer, the weather is 

 as hot as within the tropics; and, in winter, the thermometer 

 for many weeks, continues feveral degrees below the freezing 

 point. 



The thermometer alfo, which meafures the degree of heat 

 in the air near the earth, will contribute towards denoting 

 when changes are likely to take place in the lower regions of 

 the atmofphere ; the hygrometer diflinguifhes the quantity of 

 moiflure in the atmofphere, and the electrometer will point 

 out the quantity of electricity which prevails in it. 



The w r ords generally engraven on the plates of the barometer 

 rather ferve to miilead than to inform ; for the changes of the 

 weather depend rather on the rifing and falling of the mercury, 

 than on its ftanding at any particular height. When the mer- 

 cury is as high as fair, or at 30 degrees, and the furface of it 

 is concave, beginning to defcend, it very often rains ; and on 

 the contrary, when even the mercury is at 29 degrees, oppo- 

 fite to rain, when the furface of it is convex, beginning to 

 rife, fair weather may be expected. Thefe circumftances not 

 being known, or not duly attended to, is the principal caufe 

 that farmers and others have not a proper confidence in this 

 inftrument. 



It muft alfo be obferved, that ceteris paribus, the mercury 

 is higher in cold than in warm weather, and commonly early 

 in the morning, or late in the evening, than at noon, which 

 fecms occafioned by the obvious caufes of the atmofphere be- 

 ing condenfed by the cold of the night, and rarefied by the 

 heat of the day. 



The 



