Meteorological Axioms, 147 



during the courfe of thirty years, partly in my Treatife and 

 Memoirs on Meteorology, and partly in the Hillory of the 

 Medical Society, the Colleftion des Savans etrangers, the 

 Journaux des Savans, de Phyfique, de France, &c. I en- 

 deavoured to negleft nothing that had any relation to me- 

 teorology, and I flatter myfelf that I have given the refult of 

 every thing that has been publifted fcr a hundred years on 

 this branch of fcience. But how tedious is its progrefs 1 

 From this aftonifliing coUeftion of obfervations I have as 

 yet been able to deduce only a very fmall number of phyfical 

 truths, which I here lay before the public under the title of 

 Meteorological Axioms. They are not drawn from the whole 

 mafs of the before-mentioned obfervations, made for a very 

 long period, and in a carclefs manner, and with very impci- 

 fe6l inftruments, but from thofe of the laft thirty or forty 

 years. They are as follow : — 



I. 



Of the Barometer. 



1. The greateft changes of the barometer commonly take 

 place, during clear weather, with a north wind ; and the 

 fmall rifings during cloudy, rainy, or windy weather, with 

 a fouth, or nearly fouth, wind. 



2. The ftate of the mercury changes more in the winter 

 than the fummer months; fo that its greateft rifing and fall- 

 ing take place in winter; but its mean elevation is greater in 

 fummer than in winter. 



3. The changes of the ftate of the barometer are nearly 

 null at the equator, and become greater the more one re- 

 moves from it towards the poles. 



4. They are more confiderable in valleys than on moutitains. 



5. The more variable the wind, the more changeable the 

 ftate of the barometer. 



6. It is lower at midnight and noon than at other periods 

 of the day : its greateft daily height is towards evening. 



7. Between ten at night and two in the morning, and 

 alfo in the day, the rifing and fulling of the mercury arc lefs : 

 the contrary is the cafe between fix and ten in the morning 

 and evening. 



U a ^ Between 



