Atmospherical Phenomena. 273 



is made to the instruments on account of their uncertainty. In 

 an investigation of this kind we must not merely keep before 

 our eyes the character of the whole season, but an accurate 

 knowledge of the whole atmosphere above us is also requisite, 

 which, from the very nature of things, is perfectly impractica- 

 ble in reference to temperature and moisture. It is true that 

 the exertions of travellers have shewn us how these relations 

 change, as we proceed from the lower to the upper strata of the 

 atmosphere ; but these investigations relate to the mean state 

 of the atmosphere, and very important errors are possible when 

 they are applied to particular cases. We know (to adduce 

 only one example) that during a certain mean state of the 

 hygrometer, rain generally takes place ; the barometer sinks at 

 the same time, and the probability of the precipitation becomes 

 greater, especially if the sky begins to be obscured by clouds. 

 But in order to predict with certainty if it will rain or clear up, 

 a knowledge of the temperature of the upper region is requisite, 

 and, as this is awanting, there must always be a great degree 

 of uncertainty in our prognostications. Supposing the tem- 

 perature at a height of 10,000 feet to be some degrees lower 

 than usual, a great precipitation would be the consequence ; 

 whereas, if the temperature should rise an equal number of de- 

 grees, the sky would clear up with rapidity. 



Thus all the meteorological phenomena of our latitudes may 

 be referred to a constant warfare of the SW. and NE. winds, 

 and according as the one displaces the other, the weather is 

 extremely different. But not only is the state of the weather 

 for single days determined by this predominance, but the cha- 

 racter of whole seasons depends more or less on the same cause. 

 A remarkable example of this kind was lately afforded us. In 

 the summer of 1833, there were very abundant precipitations 

 throughout the whole of western Europe; the SW. winds pre- 

 dominated to a great extent, and constantly drove back the east 

 winds with violence. While in this manner continual cold rains 

 fell to the ground from the upper strata of the atmosphere, the 

 warmth of summer was repressed, and thus the month of Au- 

 gust was distinguished by an extremely low temperature. At 

 the end of that month movements of the most violent kind oc- 

 curred in the atmosphere, — storms raged in the West Indies, 



