UNITED STATES (CLIMATE). 



735 



In the Southern States, including Virginia, the Ca- 

 rolinas and Georgia, the cold gradually diminishes, 

 and to the south of the Potomac there is but little 

 snow except on the mountains. The winds which 

 chiefly prevail, are the north-west, south-west and 

 north-east. The first, which blows from the moun- 

 tains and high table land, predominates in winter, and 

 is by far the driest and coldest ; but along the Atlan- 

 tic coast, where it meets warm clouds and warm cur- 

 rents of air, it produces snow, hail, and sometimes 

 rain ; along the banks of the Mississippi and Ohio 

 rivers, it produces rain in winter and storms in 

 summer. The south-west wind prevails in summer, 

 and is more constant on the western side of the 

 Alleghany mountains than on the Atlantic coast. 

 In the basin of the Mississippi, it is said to prevail 

 throughout the year, except during two months 

 about the winter solstice. The north-east wind, 

 crossing a great extent of sea, brings cold and mois- 

 ture on all the Atlantic coast. Proceeding south- 

 wardly, however, its effects are found to diminish. 

 Its course is directed, in some measure, by that of 

 the mountains, and the space over which it blows 

 is sometimes marked by the snow which it deposits. 

 When North America first began to be colonized 

 by the Europeans, it was soon discovered that the 

 temperature of any given latitude was much more 

 rigorous than in the same latitude in Europe. Dif- 

 ferent explanations have been given of this pheno- 

 menon, of which the following are some of the 

 most striking circumstances. Humboldt has en- 

 deavoured to connect the system of climates of the 

 old world with that of the new, by fixing, at every 

 ten degrees of latitude, under different meridians, 

 a small number of places, whose mean temperature 

 has been correctly ascertained, and through these, 

 as so many standard points, supposing certain lines 

 of equal heat, or isothermal lines, to pass. The 

 observations which have been made on the tempe- 

 rature of places in the eastern and western conti- 

 nents, show that, advancing seventy degrees to the 

 east or west, a sensible alteration in the heat of the 

 atmosphere is found. Places situated, however, 

 under the same latitudes in America and Europe, 

 do not differ so many degrees as has been commonly 

 supposed. The following tables indicate the dif- 

 ference of climates expressed by that of mean tem- 

 perature, and by the number of degrees which it is 

 necessary to go northward, in Europe, in order to 

 find the same quantity of annual heat as in Ame- 

 rica ; the differences under the column of latitudes 

 are the differences between the latitude of a place 

 in Europe and a place in America, which have the 

 same mean temperature ; and the differences under 

 the column of mean temperatures are the differences 

 between the mean temperature of a place in Europe 

 and of one in America, having the same latitude. 

 As a place could not be found in the old world, 

 whose mean temperature was 58, the same as that 

 of Williamsburg, Humboldt supplied it with an in- 

 terpolation between the latitudes of two points, 

 whose mean temperatures are 56-5 and 59-4. 



1. Parallels of Georgia, Mi&nssippi, Lower Egypt 

 and Madeira. 



Natches, 



Funchal, 



Orotava, 



Rome, 



Algiers, 



Difference, 



2. Parallels of Virginia, Kentucky, Spain and 

 Southern Greece. 



Williamsburg, 

 Bordeaux, 

 Montpellii-r, 

 Rome, . . 

 Algiers, 



Difference, 



Latitude. 

 38 8' 

 44 50 

 43 56 

 41 53 

 36 48 



Mean Tern 

 , 58 tf 

 56 5 



59 4 



60 4 

 70 



3. Parallels of Pennsylvania, Jersey, 

 Lutium and Rumelia. 



Philadelphia, . 

 New York, 

 St Malo, 

 Nantes, 

 Naples, 



Difference, . 



Ipswich, 



Cambridge,(N. E.) 



Vienna, 



Manheim, 



Toulon, 



Rome, 



Difference, 



Latitude. 



39 5ff 

 40 40 



48 39 



47 13 



40 50 



7 0' 



42" 38- 



42 25 



48 13 



49 29 



43 7 



41 53 



6 30' 



7" 7' 

 Connecticut, 



Mean Tem 

 . 54 y 



53 8 

 . 54 5 



54 7 

 . 63 3 



9 5' 



11 0' 



4. Parallels of Canada, Nova Scotia, France and 

 Southern Germany. 



8uebec, 

 P-iM. 

 Padua, 

 Paris, . 



Difference, 



Latitude. 

 46 47' 

 49 51 

 45 V4 

 48 50 



13 ff 



5. Parallels of Labrador, south of Sweden and 

 Courland. 



Nains, 



Okak, . 



Umea, 



Enoutekies, 



Edinburgh, 



Stockholm, 



Difference, 



Latitude. 

 57 0- 

 57 20 

 63 50 

 68 30 

 55 58 

 59 20 



11 0' 



Mean Temp. 

 26" 4' 

 29 8 

 33 3 

 27 

 47 8 

 , 42 3 



17 1' 



By an analogous method, he found that the iso- 

 thermal line of 32 passes between Uleo and Enou- 

 tekies, in Lapland (lat. 66 to 68), and Table bay, 

 in Labrador (lat. 54) ; 2. that the isothermal line 

 of 41 passes by Stockholm (lat. 60) and the bay 

 of St George, Newfoundland (lat. 48); 3. that 

 the isothermal line of 50 passes by Belgium (lat. 

 51) and Boston (lat. 42 30') ; 4. that the iso- 

 thermal line of 59 passes between Rome and 

 Florence (lat. 43) and near Raleigh (lat. 36). 

 The direction of these lines of equal heat gives for 

 the two systems of temperature known by precise 

 observation, viz. that of the middle and west of 

 Europe and that of the east of America, the follow- 

 ing differences ; 



In tracing the directions of the isothermal lines 

 from Europe to the Atlantic countries of the new 

 world, they are found to have the character of 

 parallelism towards the south, and to converge to- 

 wards the north, particularly between the thermo- 

 metric curves of 41 and 50. In pursuing these 

 lines to the west, the thermometric means prove 

 that they do not again rise, the quantity of heat 

 which each point of the globe receives under the 



