262 Professor Kaemtz on the more important 



at any place on the plains of Germany, always shew that the 

 SW. and W. are the winds during which it rains most abun- 

 dantly, while the easterly winds are much more rarely associated 

 with falls of rain. The changes of the pressure of the air stand 

 in such intimate connection with the transitions from a serene 

 sky to a troubled one, and to rain, that the barometer has been 

 justly named the weatherglass, and it seems to me advisable to 

 consider both phenomena at the same time. 



The Barometer ajidits connection with Temperature. — A short 

 time after Torricelli's experiments, Guericke and other observers 

 remarked that the length of the column of mercury in the baro- 

 meter is in general greater in serene weather, than when there is 

 wind and bad weather; and thenfoUowed fact after fact, and theo- 

 ry after theory, until De Luc's theory was received as the correct 

 one by meteorologists, accordingto which the lighter vapours de- 

 press the barometer, — a closer examination of all the relations, 

 however, proved, that in this instance a secondary phenomenon 

 had been confounded with the principal matter. The changes 

 of the barometer may be referred to an extremely simple fact, 

 and although we may not be prepared to account for the oc- 

 currence of every single phenomenon, yet the cause of this lies 

 chiefly in the want of simultaneous observations made at remote 

 places. Originally this instrument only indicates to us the dif- 

 ference of temperature of districts, which, according to circum- 

 stances, are more or less remote from one another. 



When I spoke of the origin of winds I mentioned the changes 

 of the barometer. So long as the temperature over the whole 

 space AB is exactly the same at the surface and at equal heights 

 above it, the air will remain in a state of equilibrium, and will 

 press with equal strength on the barometer, but when the space 

 EF is unusually heated, a portion of the atmosphere lying above 

 EF descends, and the barometer must necessarily sink, while 

 it rises at AE and FB. 



The reverse would have taken place if the air above EF 

 had become colder than above AE and FB, for then the 

 atmosphere would have contracted, and as air would have 

 rushed into the empty space so produced, the barometer above 

 E F must necessarily have risen. We also perceive that an 

 unusual degree of warmth for the season is connected with a 

 depression of the barometer, and a cooling of the air with a ris- 



