CxEOGRAPHY. 9 



conversion of Reaumur's scale into that of Fahrenheit, may readily be 

 effected by multiplying f and adding 32°. To make the conversion from 

 the Centigrade or Celsius scale to Fahrenheit, multiply by f and add 32°, 

 Isothermal lines are those which connect places of the same mean summer 

 temperature, and isocheimonal, similar lines expressing the same mean 

 winter temperature. On some isothermal lines will be found marked the 

 corresponding mean summer and winter temperatures. As a general rule, 

 the cold increases both with the latitude and the elevation above the sea. At 

 a certain elevation above the latter, the snow never melts, even in the hottest 

 parts of the year. The boundary above which snow always exists, or the 

 lower line of perpetual snow and ice, is called the JSnoiv line. This possesses 

 different elevations at different latitudes, sinking deeper and deeper with 

 increase of latitude, until near the poles it comes down to the level of the 

 sea. 



The vegetation of a country depends greatly upon the mean annual 

 temperature ; still more upon the mean summer and winter temperature. 

 The differences in respect to the vegetation of different sections of 

 country, we have endeavored to express on our chart. The lines 



indicate the northern or polar limits of various plants, 



as of trees (Baume), grain (Getreide), fruit trees (Obstbaume), vine 

 (Weinstock). and the olive (Oelbaum). In western France the culture of 

 the vine extends only to 47° 20' N. L., in Champagne to 50°, on the Rhine 

 to 51°, at Griinberg in Silesia almost to 52°, &.c. The extent over which a 

 particular plant is met with, is called its circle of distribution : the extent 

 from north to south is its zone of latitude, that from east to west the zone of 

 longitude. From this is to be distinguished the vertical distribution of a 

 plant, or its region, that is, the limits of maximum and minimum height above 

 the level of the sea. Within the Arctic circle, the woody vegetation dwindles 

 down to mere shrubs, no trees being present. Arable land, too, is present in 

 only a few places. The most northern European cerealia are barley and oats ; 

 south of these we find rye, which in Norway and Sweden is met with up to 

 66°-67°. The two first-mentioned grains constitute the principal articles of 

 food in northern Sweden, Norway, and Scotland ; rye, in southern Sweden, Nor- 

 way, and Scotland, in ]5enmark, in the regions of the Baltic, and in the greater 

 part of Germany ; Avheat in England, France, southern Germany and Hunga- 

 ry. In addition to wheat, rice and Indian corn are cultivated in Portugal, 

 Spain, south France, Ital}^, and Greece. 



In conclusion, the chart presents the height of numerous points above' the 

 level of the sea, expressed in French toises. The figures at various points of 

 the ocean indicate the depth in fathoms of six feet. Remarkable inequalities 

 in the bottom of the sea are indicated by shaded lines ; an illustration may be 

 seen on the map extending from the west coast of Sweden through the Atlan- 

 tic Ocean, to the West of Great Britain, France, Sec, where we observe such 

 numbers as 250 and TO, 300 and 65, 140 and 70, close together, indicating a 

 very sudden change in depth. (These general remarks, in explanation of the 

 physical chart of Europe, apply equally to the physical charts of Asia, Africa, 

 and America.) 



9 



