250 Professor Kaemtz on the more important 



cooled. Both these phenomena are much more striking, when 

 EF is heated, and AE and FB are cooled, at the same time. 



From the foregoing, the following two laws may be deduced, 

 and they are among the most important in the whole range of 

 Meteorology : — 



1. If two neighbouring parts of the earth have unequal tem- 

 peratures, we find that, in the upper regions of the atmosphere, 

 there are winds which blow from the warmer to the colder 

 part, while, near the surface of the earth, there are winds from 

 ihe colder to the warmer portion. 



2. When a tract of the earth is unusually heated, or if it is 

 distinguished from the neighbouring regions by a high tempe- 

 rature, the barometer sinks ; but if, on the other hand, its 

 temperature is unusually low, the pressure of the atmosphere 

 increases. 



Winds. Sea and Land Breezes. — These two laws just men- 

 tioned, which follow from the simplest principles of mechanics, 

 are abundantly confirmed by experience. If, for the present, we 

 confine ourselves to the first, we find a proof of its truth in the 

 land and sea breezes, that is, those winds which, on the coasts, 

 and especially between the tropics, blow during the day from the 

 colder sea to the warmer land, and during the night from the 

 colder land to the warmer sea, and also in the frequently very 

 violent gusts of wind which proceed in all directions from a 

 thick storm-cloud. But the trade winds between the tropics 

 are the most remarkable proofs of this law. 



Trade- Winds. — Over both the great oceans extending from 

 pole to pole, there blows, during the whole year, with very rare 

 exceptions in low latitudes, a regular east wind ; this wind is in 

 general north-east in the northern hemisphere, and south-east in 

 the southern hemisphere; its polar limits lie between latitude SO" 

 and 30°. Near the equator, there is a zone where there are no re- 

 gular winds, and where calms alternate with violent tempests. It 

 is here that the masses of air rise from the surface to the higher 

 regions, and cause a powerful ascending stream of air. The 

 first voyagers who ventured far into the Atlantic Ocean, Co- 

 lumbus, Vasco de Gama, &c., were not a little astonished at the 

 great regularity of the east wind, which was a great assistance 

 to them in their voyage towards the new world, but seemed to 

 them just as great a hindrance duwng their return to Europe, 



