Attnospherical Phenomena. 271 



wind made their appearance, the sky became anew obscured, 

 the radiation ceased, and while the barometer sank a thaw fol- 

 lowed. 



The most violent movements of the barometer occur during 

 storms ; and we find a rapid depression during sudden south- 

 west storms, but a rapid elevation during storms from the north- 

 east. But although these phenomena may be readily explained 

 by differences of temperature in different regions, yet it is sel- 

 dom possible to compare the cause and effect, and in this per- 

 haps lies the reason, that the view offered above regarding the 

 connection of temperature and the pressure of the air, was of- 

 ten brought forward by the older natural philosophers, but al- 

 ways again renounced ; and that recourse was often had to the 

 most extraordinary hypotheses. The difficulty of the investi- 

 gation consisted chiefly in this, — that violent movements of this 

 kind sometimes occurred simultaneously over a large portion of 

 the earth ; and that there were seldom the requisite observa- 

 tions made in remote places. Hence we not unfrequently find, 

 that the barometer has sunk throughout the whole of Europe 

 during a temperature which is unusually high for the season of 

 the year ; but it is only necessary to turn our eyes to other re- 

 gions (a thing not easily done owing to the reason mentioned 

 above), and we find a comparatively equally great elevation dur- 

 ing great cold. Thus there was a very low minimum in one 

 instance of this kind in Europe ; but in Petersburg, and still 

 more in Moscow, the mercury was at its mean height. At the 

 same time, there was a dreadful cold on the east coast of Ame- 

 rica, probably accompanied by a high state of the barometer ; 

 observations at Bagdad, shewed great pressure of the air and se- 

 vere cold, but farthereast,at Calcutta, the barometer was very low. 



This fact shews us, not merely that unusual changes of the 

 weather extend over a large portion of the earth, but also that 

 the investigation of separate phenomena will be possible, only 

 when a series of observations from all quarters of the globe can 

 be made the subject of comparison. In connection with this 

 gubject, there is also the difficulty of satisfying the wish of the 

 learned and the unlearned, to predict the state of the weather ; 

 and I shall now add a few words on this point. 



Prognostications of the Weather. — In this problem it is 



